Manga / Sleepy Princess in the Demon Castle

The stuff of nightmares herself.

Tragedy has struck the Kingdom of Goodereste, for their beloved princess, Aurora Syalis Goodereste, has been captured by the Demon King Twilight, who has declared that he will only return her if the humans surrender the world to him. A coalition of heroes is then assembled to rescue the princess, led by her childhood friend Sir Dawner; unfortunately, because their leader is such a scatterbrain, rescuing her might be tougher than it is supposed to be.

Meanwhile, things aren't exactly smooth sailing for the Demon King and his cohorts either, because as it turns out, their hostage is quite the troublemaker. Worse still, whenever she's not causing all sorts of problems, she'll often sleep the day away... and when she's aroused against her will, somehow being attacked by the hero's party will become the least of their problems.

Sleepy Princess in the Demon Castle (魔王城でおやすみ, Maōjō de Oyasumi, literally Sweet Dreams in the Demon King's Castle), is a genre mix of Slice of Life, comedy and high fantasy written and illustrated by Kumanomata Kagiji since 2016 for Shogakukan's Weekly Shonen Sunday series and licensed for English release by VIZ Media. It also has an anime adaptation directed by Mitsue Yamazaki for Doga Kobo, premiering in October 2020.

Has nothing to do with Sleeping Princess in Devil's Castle, the second Non-Serial Movie in the Dragon Ball franchise.

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Tropes:

• Adam Smith Hates Your Guts: When the demons escort the princess to the nearest human town so she can purchase a limited edition pillow, they find that everything is extremely expensive because the nearest human town is, from the humans' perspective, the Hero's last stop before the Very Definitely Final Dungeon, and all the prices are inflated accordingly.
• Adaptation Deviation:
  • The reason and way the Princess gets her Tire Demon armor is different in the manga and the anime. The anime has her needing something to cover herself in to endure the coldness of the Ice Area, with her seeing the Tire Demon and then attacking him with her giant pair of scissors. The manga, meanwhile, has the Princess already having the armor at this point, as she originally needed it to allow the Thunder Dragon to apply some electric shock to her stiff shoulders without killing her (especially considering how the original attempt resulted in her getting punished in the form of the Demon Cleric keeping her dead for a week the next time she died), with her gaining it via an army of Teddy Demons attacking the Tire Demon.
  • The ultimate origin of the Princess's signature which Sir Dawner uses to travel into her dreams also differs. In the anime, it's one of the autographs she hands out to the Teddy Demons, while in the manga it's one of the items from an area she designed at the demons' request. However, Sir Dawner gets his hands on it the same way in both of them, when the Demon King accidentally drops it in front of him.
• Adaptation Expansion: The anime adds several extra details to each of the manga chapters' stories. The main points being the addition of near-constant internal monologues and talking to herself from the Princess in the earlier "nights", where in the manga it only pops up occasionally, usually at the beginning and end of each chapter, and elaborating on Dawner's Hero of Another Story status by showing more of the various parts of his journey than the manga already did.
• Adaptational Early Appearance:
  • Episode 5 of the anime includes content from Chapter 37 of the manga, introducing Neo Alraune and Poseidon to the story a lot earlier.
  • Episode 8 introduces Succyun during the dentist segment (Chapter 58 of the manga), where she'd originally been introduced in Chapter 74.
• Affably Evil: Despite nominally being the bad guys, the demons are all incredibly friendly and polite both to each other and also the princess they kidnapped, to the point they'll readily let the princess walk all over them in her unhinged quests for a better night's sleep.
• All Love Is Unrequited: As the story goes on, there are an increasing number of characters that pine for others that are completely oblivious to their affection, while also being oblivious to the affection of people pining for them. The Princess herself has the attention of Hero Dawner, Demon Cleric Leonard, and Stray Kamaitachi. Meanwhile, Twilight is pined for by Dragon Lady Zetsuran, while Zetsuran is pined for by Sand Dragon.
• Always Chaotic Evil: While the Demons of now are friendly, it has been repeatedly mentioned that before, they were more or less genuinely evil and wars were caused between them and the humans. This naturally caused a divided line between the two races. Those like Twilight and even his father at one point tried to bridge the two races in the past.
• April Fools' Plot: In chapter 94, the Princess takes the Demon King's April Fool's prank seriously, thinking the castle's about to be destroyed, and the demons have to convince her it's not actually true.
• Attack of the 50-Foot Whatever:
  • The Princess in chapter 59, although it's only temporary.
  • In chapter 61, the Princess's Eggplant Seal evolves into a larger form. A much larger form.
  • Former Demon King Midnight grows as he accumulates magical energy, and is giant-sized until the stored up mana ends up getting sucked away thanks to Alazif's Grimoire Rhinitis (and the Time Travel adventure the Princess and the Cursed Musician have become of it).
  • Twilight and Zeus grow to giant size in chapters 330-331, but again, it's temporary.
• Background Body Part: The cover of volume 3, which has a blood-red crescent moon positioned in just the right spot to make it look like the princess has horns.
• Baku: In the castle's basement is a Bakumu and an army of Nightbears. A Nightbear is a teddy bear-like monster that eats the nightmares of the castle's residents and converts it into nightmare fog which feeds the tapir-like Bakumu. In Chapter 22, the Nightbears are too busy collecting nightmares about the Princess — her antics around the castle causing bad dreams for the monsters that live there — to do their jobs properly, thus causing indigestion for the Bakumu and bad dreams for everyone else. It is not until the Princess grooms the Nightbears that things return to normal.
• Be Careful What You Wish For:
  • According to the volume 2 extras, the baku wanted quantity over quality for nightmares... then the Princess showed up, and he ended up getting so many nightmares he got indigestion.
  • The demons spend an entire week trying to get the Princess to act more like a hostage, but every plan fails. The one plan that does seem to work though ends up backfiring as everyone becomes hurt and depressed at having the Princess treat them like vile monsters (even though she was faking it).
• Bifauxnen: Raikou, unknown to the demons.
• Bland-Name Product:
  • Chapter 319 features the Princess shoving a copy of Shonen Someday (parodying Weekly Shonen Sunday, the magazine both this series and Call of the Night were running in) in Twilight's face.
  • In Chapter 320, the Princess discovers the Teddy Demons run an Ubear Eats delivery service.
  • Invoked in Chapter 325, where Super Demon King Kart is mentioned to be the Demon World version of a "mega-popular human video game".
• Bond Villain Stupidity: While humanity and demonkind are at war and The Hero is regarded as the official enemy of the Demon King, the Demon King purposefully leaves key items and helpful things laying around with minimal security — including a Mechanical Monster with a built-in, easily exploitable weakness — specifically because he wants the honor of killing the hero himself.
• Box-and-Stick Trap: The Demon King uses a variation of one involving a steel cage to recapture the Princess after an escape attempt (because she wanted to go shopping in the human realm). There was a futon inside the trap, and it closed when she fluffed the pillow.
• Butterfly of Doom: Chapter 200 has Alazif coming down with Grimoire Rhinitis, which causes him to perform Accidental Time Travel with Princess and Cursed Musician whenever he sneezes. After the second sneeze, he brings them to an Alternate Timeline where, due to the Princess stealing his special futon that Demon Cleric gave him, the Demon King decided that it meant he needed to grow up and be independent from relying on Demon Cleric and Hades, resulting in him bringing about massive changes to the Demon Army, starting with kicking out the weakest demons such as Teddy Demons and Eggplant Seals. In order to fix things in Chapter 203, the princess not only returns the futon, but also explains that the Demon King is not alone in caring greatly for Demon Cleric, making the young king stop thinking about changing things.
• Came Back Wrong: With the amount of times that the Princess dies and has to be resurrected, it was inevitable that sometimes it would go badly:
  • Early on, the Demon Cleric botches a mass resurrection spell and accidentally fuses the Princess with a Stamper Cat demon. The fusion itself is actually easy for him to repair; the problem is that the Princess wants to take the opportunity to take a nap under her kotatsu while in a cat body and resists the Cleric's attempts to heal her.
  • Chapter 214 starts off with the Princess dying yet again, with the Demon Cleric putting her tombstone in a coffin. However, before he can revive her, he is asked by the Demon King to take part in a three-day business trip. As such, the Princess remains dead for longer than usual, which results in her becoming a zombie, complete with a desire to eat brains and displaying various zombie-based behaviors, all while she tries to use this as an excuse to sleep like a zombie. In the process of trying to experience zombie sleep, she almost causes a Teddy Demon Zombie Apocalypse before Demon Cleric finally gets things under control and returns everybody to normal.
• Card-Carrying Villain: The demons are officially evil, more or less because it's part of their job spec. And while they can be brutal dealing with human heroes that try to rescue the princess, they otherwise seem to limit themselves to harmless villainy.
• Cardboard Prison: The demons might as well leave the Princess's cell door open for all the good it does (if nothing else, the Teddy Demons will just give her another copy of the key in exchange for another round of brushing). Later on, they just stop caring as long as she isn't wreaking havoc. It's even shown that the Princess, in spite of her penchant for escaping custody, has no intention of leaving Demon Castle even when she has all the capacity to do so, and then some - whenever she leaves the castle proper, it's to perform some errand, and she returns the moment it's done.
• Casting Gag: Chikahiro Kobayashi once again voices an anthropomorphic wolf, this time without the massive baggage.
• Childhood Friend Romance: In a manner of speaking. The princess and the hero are childhood friends and are engaged... but the princess doesn't even remember the hero's face or name (and doesn't really care to remember) because he apparently made so little of an impression on her when they were young (her image of his face is henohenomoheji, representing anonymity).
• Christmas Episode: Syalis writes a letter to Santa asking for a high-tech sleep pod, and knits a stocking large enough to hold it. However, the demons unanimously agree that she's the naughtiest person they know, and she wakes up in the morning to find the stocking full of coal and potatoes. The following chapter, she tries to win that pod by rigging the bingo tournament at the Castle's Christmas party (which she also uses to get rid of all the coal and potatoes), but she falls asleep during the Demon Cleric's interminable speech early in the evening. The pod was won by Ice Golem, who turned it into a bobsled. The following year, the Christmas arc centers around the demons taking the Princess back home so she can retrieve her winter wardrobe. The year after that, the demons decide to play Santa for her after she gets another stocking of coal and potatoes. The fourth year, the Princess spends the new year at Quilladillo's family home.
• Coincidental Accidental Disguise: The Princess's Tire Demon armour gets covered in frost while exploring the Ice Region in search of some way to cool her cell. The inhabitants mistake her for their area boss Ice Golem, which she exploits to get an igloo constructed in her cell. She also takes advantage of the resemblance on subsequent visits.
• Comedic Sociopathy: Courtesy of the Princess. She has free run of the Demon King's castle, and regularly terrifies its inhabitants, but it's all in the name of nothing more than a good night's sleep. It's eventually made clear that she's too absentminded to be actually malicious, so most of the time she doesn't realize that she's harming others or herself.
• Contrived Coincidence: Whenever the Princess has an obstacle to her objective, a demon with just the right ability will show up in front of her. And whenever demons discuss a magical item you can bet the Princess is in the middle of breaking/stealing it.
• "Could Have Avoided This!" Plot:
  • The plot of chapter 58 has the demons trying to fix the Princess's cavity, but it ends up taking eight hours because she'll only let a Teddy Demon look at her mouth. Once it's all over, the demons realize that they could just have waited until she fell asleep and done it then.
  • The plot of chapter 90 involves the Princess and Poseidon doing their best to avoid getting flu shots due to their shared fear of needles. At the end, after they're finally caught and given the shots, it's pointed out if they had Hi-Potions, the shots wouldn't have been necessary. Except the Princess drank so many of them that year they didn't have enough and had to resort to the injections, with the realization that their problem was all her fault causing the Princess to earnestly apologize to Poseidon for the incident.
• Dark Horse Victory: The winner of the Castle's summer festival beauty pageant is Harpy, who went completely unnoticed in the face of the other contestants (the Princess, a slime, a number of zombies, and the men of the Castle in drag, trying to prevent the Princess winning).
• Death Is Cheap: Thanks to the Demon Cleric's ability to revive the dead, the poor souls the Princess uses for material are generally okay. Heck, the Princess herself has died a few times in her search for a sleeping spot. In spite of this, the mental and physical toll on the Demon Cleric incurred by the Princess is enormous, as she's killed a mountain range's worth of demons on her own. At one point the Princess is shown delivering a laundry basket full of demons she'd killed over the past week to the Cleric for resurrection - with a statement that this is a part of their weekly routine.
• Demoted to Extra: The Fruit Demons get demoted from fairly minor characters who drop out of the story fairly early on in the manga to having a ten second cameo in the opening credits of the anime without any of their stories being animated at all.
• "Do It Yourself" Theme Tune: Inori Minase (Syalis) performs the opening theme, "Kaimin! Anmin! Syalist Seikatsu" ("Good Rest! Sound Rest! Syalist Life").
• Dub Name Change: In the original manga, the royal family's surname is "Kaymin", a pun on kaimin, meaning "good sleep"; Viz changed it to the English equivalent "Goodereste" for their translation (with Funimation also using "Goodereste" for the sub of the anime).
• Embarrassing Old Photo: Chapter 132 sees both the Demon King and Demon Cleric trying to retrieve photos of their embarrassing pasts from the Former Demon King's Castle. Unfortunately, the Princess got there first in her search for high-class bedding.
• Entertainingly Wrong: At first, the demons believe the only reason the Princess is assaulting them and breaking out is that she wants to escape. It takes a fair while for them to understand that her only concern is getting some rest. This, however, turns into the demons going on logic tangents that involve the princess ranging from her romancing them to hurting them, and always being wrong in said assumption.
• Expository Theme Tune: The opening theme of the anime adaptation, "Kaimin! Anmin! Suya Rhyst Seikatsu" (Good Rest! Sound Rest! Syalist Life!), has the Princess explain the premise of the plot: She's a kidnapped princess imprisoned alone in the Demon King's castle with nothing to do but sleep... but her accommodations suck. So now she's going to do whatever it takes to get a good night's rest.
  Princess: How would you like to be bedding too?
• Failed a Spot Check:
  • Hades manages to completely miss the havoc the Princess causes when she's at his place, including a notable incident where she ripped apart his robes to make pillows - while he was wearing them.
  • The Princess completely misses the creatures that are scaring her in the ghost stories she's reading are herself and the castle demons.
  • While playing Leave Forest, the Princess walks past the in-game shop without noticing it, and comes to the conclusion you can get stuff by taking it from other people, causing her to go on one of her Kleptomaniac Hero sprees.
• Forbidden Love: Harpy, trying to be friends with the Princess, tries to ask who the Princess has feelings for. She first asks if it's the hero before wondering if she has developed a forbidden crush on a demon. The Princess ignores her and doesn't answer.
• Forced Sleep:
  • At one point, the princess casts a high level sleep spell, only for it to knock out everyone in the castle except her.
  • Continuing with the title's homage to Sleeping Beauty, one story arc involves Poseidon falling into a deep sleep when, while trying to prevent an Eggplant Seal from pricking itself on the spindle of a magical spinning wheel, he ends up getting pricked himself.
• Fountain of Youth:
  • The Princess stumbles on one while looking for something to make her smaller, and it temporarily turns her into a kid. When she tries to replicate the effect, she inadvertently turns all the demons in the castle into kids instead. Eventually she replicates it successfully, because she wants to test the demons' ways of lulling a kid to sleep, only to find most of the demons are missing (having gone to the new confectionary shoppe), so she tries going to sleep on her own, before remembering that in the past she couldn't get to sleep without someone lulling her... and the only people around are Cursed Musician, Zeus, and M.O.T.H.E.R., who aren't exactly cut out for the job.
  • As a result of his mana getting sucked by Alazif's Grimoire Rhinitis, Former Demon King Midnight's body ends up reverting to that of a 2nd or 3rd grade kid. Obviously, he isn't too happy about this.
  • Twilight and Zeus end up as babies in Chapter 333, thanks to using most of their magical energy during an earlier escapade.
• "Freaky Friday" Flip: The Demon Cleric sometimes has this happen to him when reviving the dead.
  • He starts wishing he could become something pure like a Teddy Demon while resurrecting one, which results in him temporarily switching souls with it.
  • Due to a lack of sleep as a result of a demon mite infestation, he winds up switching bodies with the Princess as he tries to revive her.
• Fun Size: A mandrake that grew out of the Princess's head ends up taking on her nature, doing whatever it can in order to have a good sleep. The Princess recognizes they're too similar to live together, and so gives the mandrake to Succyun to look after.
• Gender Bender: The entirety of the Castle's population gets hit by a magical sex change in Chapters 312-313, and for once it's not Syalis's fault. Twilight gets hit by a deliberate sex change in Chapter 316 as an emergency disguise.
• Gilded Cage: For all that the people of Goodereste worry about her, Syalis is well cared for by her alleged captors. She eats better than most of the demons do, and nobody ever seeks to harm her. Every injury she suffers is the direct result of her going on an adventure to improve her sleeping conditions instead of staying in the quarters she's supposed to be locked up in.
• Gods Need Prayer Badly: In this story, the level of power a god currently holds is directly proportional to the amount of faith and prayer they receive from humans at any given moment. For Poseidon, under normal circumstances he has enough faith to be reasonably powerful but nothing special, but on "Marine Day", a holiday during which faith in him is at an all-time high, his power skyrockets, along with him transforming into an adult form.
• Good Angel, Bad Angel: Happens to the Princess when she becomes torn between Quilladillo's health, and not wanting him to get sick due to being overweight, on the one hand, and on the other, still wanting him to have a springy tummy that she can sleep on.
• Go-to-Sleep Ending: While every episode of the anime has the princess fall asleep at the end, they don't count because there would usually be a bit more afterward from the other demons before each episode officially ends. However, the last part of episode 12 plays this straight; in which after the princess falls asleep (with a bunch of other teddy demons), the camera pans out to the outside of the castle with the narrator wishing her sweet dreams before the episode ends.
• Green-Eyed Monster: The demons get jealous of the Princess getting starry-eyed over the athlete Raikou, and try doing everything they can to catch her attention. She ignores them.
• Half-Human Hybrid: Narmie is half-human, half-demon.
• Holy Halo: When the Princess becomes mellow because of the mandrake growing out of her head in chapter 80, the demons imagine her with a halo making hand signs like a Buddha statue.
• Homage: Invoked in Chapter 319, as Syalis stages the scene from Call of the Night where Kou first meets Nazuna as an intervention for Twilight, complete with adopting Nazuna's trademark hairstyle and personally installing a vending machine.
• Horned Humanoid: Multiple demons look like humans with various types of animal horns on their heads. This includes the Demon Cleric having goat horns, Demon King Twilight and Former Demon King Midnight having bull horns, and Hades having antelope horns.
• Hot Springs Episode: Chapter 39 features the Princess digging a hot springs in the castle basement - flooding a good part of the place in the process, not that she cares. Later on, chapters 97-101 form a hot springs mini-arc, with chapter 97 about the demons getting ready for the trip, chapters 98-100 about what happens at the springs, and chapter 101 about the trip back.
• Human Subspecies: Long ago, the dark gods attempted to wipe out a certain species. Some of them, protected by the divinities, escaped to become the first humans. Those who remained were slaughtered by the dark gods, with the few who managed to survive getting transformed by the dark gods' magic power and becoming demons.
• Humans Are the Real Monsters: While the demons hold Card-Carrying Villain attitudes, constantly proclaiming themselves evil, as a whole they're mostly harmless, while time and time again it's shown that the humans are much, much worse, even though most of the humans aren't deliberately malicious. For some examples, the Princess is so obsessed with sleep she has a habit of slaughtering demons by the dozen daily in her efforts, while Sir Dawner is so obsessive in his desire to marry the Princess that he borders on being a Yandere.
• Hypocritical Humor: It takes a while for the Princess to clue in that the things she complains about the mandrake doing are the exact same things she does.
• Identical Stranger: As shown by Succyun and Incyun, the Succubus family all look practically identical to members of the Goodereste family, in particular Succyun looking like the Princess and Incyun looking like the King. Though based on those two, each of them are an Oddball Doppelgänger, being nothing like their respective royal member in personality.
• Idiosyncratic Episode Naming: The manga and anime use the format "[X]th Night: [Title]", e.g. "78th Night: Princess Runnings". (The scanlation uses "The [X]th Night".)
• Inconsistent Spelling: Is the Princess's name "Syalis", "Suya Rhys", or "Suyaris"? According to the Viz translation, her full name has it as "Sya Lis", but everyone in-universe goes with "Syalis".
• Incredible Shrinking Man: The Princess uses a magical item to temporarily shrink herself so she can sleep on a Teddy Demon's stomach, and ends up causing a lot of trouble for the Demon Cleric.
• Innocent Innuendo:
  • The Princess ends up causing a mass nosebleed epidemic in chapter 40 by asking everyone if they love her (because it was Valentine's Day and she wanted chocolate to help her fall asleep, having no idea what it means when a girl her age asks people if they love her).
  • Becomes something of a running gag, as often the Princess will want something mundane only for it to sound like flirting or even a sexual proposition. Such as the time she wanted to sleep in other demons' beds to see how they feel.
• Instant Gravestone:
  • Whenever the Princess dies, she turns into a gravestone with a little crescent moon on the top... despite the demons turning into various types of regular corpses and skeletons whenever they're killed by her.
  • Chapter 260 has Harpy also become one after dying, along with revealing that the Princess turning into a gravestone upon dying is why Death Is Cheap for her and a few other fleshy characters, as it perfectly preserves their body for revival by a priest eventually. Said chapter also has Harpy noting that if somebody's gravestone can't be retrieved for revival, said person is effectively Killed Off for Real.
  • Chapter 275 has Silmoth become one when she dies, dropping lots of silk items in the process.
• Intercontinuity Crossover:
  • Komi Can't Communicate has an omake where the titular Komi finds herself in the castle and meets the Princess, and in true fashion, is captured by the demons for safe measure (though as far as Komi's concerned, it's All Just a Dream), while this series has an omake where the Princess travels to Komi's world for a short while.
  • Chapter 188 is a crossover with Doraemon to mark its 50th anniversary, having the Princess nick Doraemon's fourth-dimensional pocket when he and Nobita accidentally arrive outside the Castle and experiment with using his items for sleeping.
  • There's another pair of mutual omakes with Fly Me to the Moon, commemorating both series' anime in the Fall 2020 season, with the Princess showing up out of nowhere to try out sleeping with Nasa and Tsukasa.
• Internal Reveal: Twilight discovers in Chapter 316 that his First Love, who he thought was a girl, was actually Dawner. He has a BSoD for a few chapters afterwards.
• It Runs in the Family: As more and more of the Goodereste royal family are revealed, it becomes increasingly clear that every female in the line, including Princess Sya Lis, Queen Nem Lis, Aunt Como Lis, and Grandma Ahm Lis, are total Cloudcuckoolanders with a penchant for Comedic Sociopathy.
• Leaked Experience: One chapter involves the demons realizing that the Princess is inexplicably of a much higher level than she should be and trying to figure out how she managed to become so powerful when she spends most of her time sleeping. It turns out to be due to this trope; she's registered as a party member of the hero who's coming to rescue her, meaning as he and his team level up, she gets a free power boost.
• Leaning on the Fourth Wall: One chapter of the manga centers around Syalis building a jury-rigged satellite dish on top of the castle so that everyone in the castle can watch the premiere of the Sleepy Princess anime.
• Lima Syndrome: After the Princess gets kidnapped from the demons and returns, it's implied the demons are starting to suffer this, worrying about what'll happen when the Hero finally rescues her. In fact, just the thought that she doesn't like them sends the demons into a massive castle-wide depression. There are also hints that some of the demons may have started to develop romantic feelings for the princess, and a Running Gag involves demons misintepreting her intentions as romantic.
• Loophole Abuse: In chapter 75, the rules of the demons' impromptu armwrestling tournament state that the winner must pin their opponent's hand to the table for three seconds. The Princess defeats Ice Golem (after... persuading his original opponent to give up his spot) by cutting off his arm and laying it on the table since the rules never said that the hand had to be attached to its owner.
• Luck-Based Search Technique: Syalis accidentally performs a three stage unlocking process to find the hidden room where an ancient grimoire is stored by falling down the stairs.
• Made of Magic: The dark gods are amalgamations of the magic power produced by living beings - more specifically, magic power suffused with fear and sorrow.
• Merging Mistake: One of the Princess's resurrections sees her accidentally get merged with a demon cat, coming back in its body. The Demon Cleric manages to undo it, but not until after the cat-Princess wrangles him into smuggling her back to her cell to spend several hours sleeping under the kotatsu.
• Money Spider: Monsters apparently drop gold when defeated in this world. The Princess planned to fund a shopping expedition to the nearest human city with the proceeds from "greeting" monsters and adventurers: her thought bubble shows 10G for a ghost shroud. She falls asleep while waiting in line for a high-tech pillow, forcing her chaperones to borrow funds from demons who lived nearby.
• Morality Pet: The Princess shows genuine affection towards the eggplant seal, treating it as if it were her child. This is a significant contrast to the treatment most demons get from her.
• New Job as the Plot Demands: A one-chapter example in Chapter 310, where the Princess keeps turning up as a worker everywhere the Demon Cleric goes, courtesy of all the shops being connected. The Cleric's left seriously discombobulated, particularly since he was trying to scope out potential "date" spots for them.
• The Night That Never Ends: It's normally eternal night in the Demon World...until Zeus was introduced. His arrival turned night into day.
• No OSHA Compliance: The demon castle is designed akin to levels from a video game and as one would expect is very hazardous, with extremely high walkways that have nothing to keep people from falling off them, and giant lava pits that serve no purpose. The old demon castle ruled by Hades is even more dangerous, being full of lava and a number of death traps. Even the demons, who don't object to the hazards in their own castle, point out that the old demon castle is dangerous.
• Non-Indicative Name: While the demons that act as commanders of the demon army under the Demon King are called the "Ten Elders", there aren't actually 10 of them in number. That's just the number of positions available to be commanders in the army. There's actually only 9 of them, though the Princess at times is considered an unofficial 10th. There was an actual 10th, but he accidentally landed himself with a long-term Perception Filter, preventing anyone from remembering or registering him, and he could only break it by making a big enough disturbance to catch someone's attention.
• Not the Intended Use: There are many items in Demon Castle which have a stated and obvious purpose, typically for adventuring, but Syalis uses them as sleep aids.
  • A magic shield that conjures wind? An air mattress.
  • A sword that glows due to its great supernatural power? A sunlight therapy light.
  • The wings of a living harpy, still attached to that harpy so she can fly? A comforter.
• No Self-Buffs: At one point, the princess casts a high level sleep spell, only for it to knock out everyone in the castle except her.
• Offer Void in Nebraska: While Syalis can watch the human shopping network from the Demon Castle, it's outside their delivery network. Multiple chapters center around the Princess seeking to reproduce some item she saw being advertised there since she can't order it.
• One Dialogue, Two Conversations: In Chapter 315, Syalis and Zetsuran talk about preparing beans. Trouble is, Syalis thinks they're talking about preparing beans to make chocolate for Valentine's Day, while Zetsuran thinks they're talking about preparing beans for Setsubun.
• Our Demons Are Different: Including such things as:
  • Teddy bears with wings
  • Literal Bed Sheet Ghosts
  • A humanoid pile of car tires
• Painting the Medium: The plot of chapter 106 involves the Ten Elders (and the princess) drawing a 4-koma manga in order to convince children to join the demon army. The time they spend drawing the 4-koma is depicted in the chapter as a 4-koma, unlike the regular manga style of the rest of the chapter.
• Pity the Kidnapper: The demons really didn't realize what they were letting themselves in for. The Princess is by far the worst thing they've ever had to deal with, but due to their vested interest in luring the Hero, they are completely unable to rid themselves of her.
• Poor Communication Kills:
  • The Princess, for all her skill at slaughtering demons, is astonishingly awful at speaking to other people. A number of gags revolve around how she simply goes out and acts, leaving everyone around her with zero context on how to handle the situation. Other times, her actions have too much context, giving everyone around her the completely wrong idea. Example: in Chapter 11, she goes around asking demons to press her pressure points for a better sleep. But because of being warned by Syberian to not make a ruckus, it devolved from 'pressing pressure points' to 'touching her in bed'.
  • Poor communication is also responsible for some of the gods' and demons' current issues. A major issue in modern demons' attempts to patch things up with humans is that humans generally don't know anything about demons and have a bad impression of their powers and religious practices, and the demons never tried reaching out and seriously engaging with them. On the divine side, Zeus never told the humans about anything that was going on because he was hung up on how lame it made him look to get weaker because of the decline in faith.
• Potty Emergency: The princess runs into one of these when the usual toilet near her cell is getting changed. She tries finding another toilet, but most of the demons use toilets that she can't use because of their species. In the end, she ends up using the Demon King's private restroom, much to the chagrin of the Demon King, who also needed to use the restroom.
• Public Bathhouse Scene: In chapter 222, the Princess, Twilight and Midnight seek out the Legendary Public Bath.
• Pun-Based Title: The Japanese title of the series, 魔王城でおやすみ / "Sweet Dreams in the Demon King's Castle", is also a homophone of 魔王女でおやすみ / "Sweet Dreams from the Demon Princess".
• Punch-Clock Villain: The majority of the demons. They're enemies of the humans because it's essentially their job, but they really aren't malicious.
• Punny Name:
  • The original Japanese name of the human kingdom and its royal family is Kaymin, punning on kaimin ("good sleep"); the official English translations keep the pun by changing the name to Goodereste.
  • The Princess's full name in Japanese is Aurora Suya Lis Kaimin, a series of sleep related references and puns that basically means "Sleeping Beauty ZZZ Good Rest".
  • In Japanese, the "Teddy Demons" are でびあくま, which can read as either "devi-devils" (でび-あくま) or a Portmanteau of "devious bears" (でびあ-くま).
  • Similarly, in Japanese a panda variant of the Teddy Demons with one demon wing and one angel wing are called パンだてんし, a Portmanteau of パンダ / "Panda" and だてんし / "Fallen Angels", i.e. "Fallen Pandangels".
  • The closest human city to the Demon Castle is called "Endopolis" in English, fitting for a human settlement that's at the "end" of the line along the hero's path to the Demon King.
• Railroading: The demons actually try to do this to Dawner, as he keeps getting lost on his quest.
• Recursive Canon: During the Princess' preparations for visiting the Royal Demon Academy, she packs in an issue of Shounen Sunday, the real life magazine that the actual Sleepy Princess manga is published in.
• Renaissance Man: Raikou's adept at a wide variety of things: fencing, athletics, cooking, archaeology, mountain climbing...
• Reset Button: If the Princess adds something to her inventory, odds are it will be removed later. Episode 4 of the anime sees her kill the Rocket Turtle and use his shell as a bathtub. Later in the episode she tricks the ice demons into making her an igloo from the Ice Golem, acting as her personal air conditioners, and giving her a trio of Eggplant Seals to sleep with. Both alterations are undone by Syberian who makes her put things back the way they were.
• Retronym: While the manga has the English words 'Sleeping Princess' alongside the title on the tankobon covers, the anime instead has the official English title alongside the Japanese title.
• RPG Mechanics 'Verse: Status conditions, experience points, and item crafting are all mentioned at different points in the series.
• Running Gag:
  • The anime has a 2 shot scene of the Princess knocking her brush against her bars, followed by the Teddy Demons floating over with the keys to her cell, over multiple quests and episodes to play up what a Cardboard Prison her cell actually is.
  • In the manga extras, every monster's favorite food is "steamed monster bird egg custard".
  • Twilight insisting that he's going to talk to the Princess right now about something she's doing, only to find her fast asleep and him not having the heart to wake her.
• San Dimas Time: During the Time Travel arc, each time they jump, time passes at the same rate in both the past and the present. However, in this case it's justified, because Alazif, the one time-traveling, is only doing so because of Power Incontinence, so each time he transports the Princess, Cursed Musician, and himself, he jumps 10 years on the dot, meaning after a day passes in the present of the Alternate Timeline, so too does a day pass in the past, which coincidentally puts them a few minutes before the Demon King's coronation, the point where the timelines diverge, giving them a limited amount of time to fix things.
• Schizo Tech: For the most part, the world seems to be a medieval fantasy world. However, things like mecha and nanomachines are apparently pretty common-place, as are the occasional modern devices like flush toilets and kotatsus.
• Self-Deprecating Humor: In Chapter 106, when brainstorming ideas for the premise of a propaganda manga, one demon offers up the premise of this manga, only for the Princess to say it sounds boring with no end and another saying it probably wouldn't be very funny.
• Sick Episode:
  • In chapter 172, the Princess tries some poison to see if it'll make her feel sleepy. Instead it makes her collapse, and the demons come to visit her in bed, all of them convinced it was their fault.
  • In chapter 317, Cursed Musician comes down with a cold, and Harpy and the Princess look after him.
• Skewed Priorities: Played for Laughs. As time goes on, it is pretty obvious that Syalis is fully capable of escaping the castle or even ending the war herself with Alazif's magic power. However, when the opportunities present themselves, Syalis is either completely oblivious to this or just doesn't care, too obsessed with her goal of the day to even consider it.
• Springtime for Hitler: In Chapter 24, it is revealed that the reason why the demons leave precious and powerful magical items in easy to access areas is because the Demon King wants to be the one to kill the hero himself, thus he wants to give the hero the edge against his bosses and flunkies. Unfortunately, almost all of the artifacts are either stolen or destroyed by Syalis before the hero ever gets to them, prolonging his quest unintentionally.
• Status-Buff Dispel: At one point the Princess is forcibly equipped with a status cancelling artifact after she gets herself killed using a giant poisonous mushroom as a mattress. To her dismay, this includes the status effect of sleep - even when it occurs naturally.
• Succubi and Incubi: There are at least two succubi/incubi, but they don't feed with sex, per se. They feed on human vitality and survive by being popular.
• Theme Naming:
  • The members of the Goodereste family have names relating to sleeping. While the given names for the three revealed so far are the same (Aurora for the Princess, her mother, and her aunt), their middle names are most notable. The Princess is S(u)ya Lis, the equivalent of the "ZZZ" onomotopoeia, referencing her frequent attempts to sleep, her mother is Nem(u) Lis, which literally translates to "sleep", and her aunt is Como Lis, which Poseidon lampshades in the extra joking that she must be a hermit.
  • The hero and his companions have names relating to waking people up. The two revealed so far are Sir Dawner (Japanese name Akatsuki, which translates to "dawn"), referencing waking at dawn, and Waker, one of his companions, which is self-explanatory.
• Throw the Dog a Bone: Chapter 224 has a dual one for both Al Azif and Succyun. In it, Al Azif finds somebody who genuinely respects him and displays awe and amazement at his incredible powers, while Succyun finally succeeded at becoming popular with somebody in the way she wanted.
• Tickle Torture: The Demon Cleric has let his bats punish the Princess with this when she's annoyed him by dying and requiring resurrection too often.
• Title Drop: Happens in episode 5 of the anime courtesy of the English dub.
  Twilight: She is quite the sleepy princess... in the Demon Castle... hehe.
• Toast of Tardiness: After taking part in a Demon Academy inspection in place of Former Demon King Midnight, the Princess and Twilight are seen doing this at the end of Chapter 218.
• Vetinari Job Security: Cursed Musician invokes this in Chapter 324, going AWOL so the Demon King will realize how much he does. In reality, he's trying to teach Odile a lesson about taking a break.
• Whole Episode Flashback:
  • Chapter 41 is set in the past, taking place a few days after the Princess first arrives at the castle.
  • Chapter 190 has the Princess dream about what actually happened with her kidnapping.
  • Chapter 347 has the Princess recall the time she had a rare opportunity to sleep with both her parents, but her father couldn't make it back home.
• World of Technicolor Hair: Both humans and demons have shown a wide variety of natural hair colors outright impossible in real life, such as the females of the Goodereste family having silvery-purple hair and several demons having green hair, which is never commented on and treated as completely normal.
• Write Who You Know: In-Universe. Chapter 212, which serves as an advertisement for the anime adaptation, involves the production of an anime series about the events of the Demon Castle, with Twilight and Great Red Syberian wanting everyone to act natural as a camera films footage for reference material. Unfortunately, almost everyone else hams it up when the camera rolls, with the only one acting natural (and thus having usable footage) being the Princess (which results in the series being about her rampages throughout the castle before she goes to sleep).
• Wrong Assumption: In Chapter 318, the human army spies on the Castle, only to interpret the various hijinks going on as evidence that the demons are their sworn enemies.

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Suya~