Fanfic / UnderVow

A demon, a monster, and a new promise to keep

It is the end of the Genocide Route. Sans and Chara, the latter now in control of Frisk after countless resets, have their final battle once again... and once again, Sans fails to defeat them. The world is destroyed and recreated once more, with no one to stop the demon.

...or at least, that's what they had thought.

Around a month or two before the main events of the game, Sans suddenly remembers every single reset. Not wanting to see everyone die again, or atleast wanting to make it atleast somewhat less easy for the "human", makes a vow to help the strongest monsters prepare for the upcoming battle.

And you can bet he is determined to keep it.

UnderVow is an Alternate Universe Fan Fic for Undertale written by ThomasTheCoolKid. While roughly based on ideas from Dusttale and Glitchtale, it does not remain constricted by either of its inspirations, attempting to create a story where all of the main characters get a chance to shine.

Later on, the writer created a technically-non-canon side story called To Render A World Unresponsive, depicting the characters' hypothetical encounter with Error Sans after the end of the original story. The writer has also promised a "second season" for the story. (Note: the folders for To Render A World Unresponsive and season 2 contain unmarked spoilers for season 1)

The story, starting from chapter 1, can be read here. To Render A World Unresponsive can be read here, and season 2 can be read here.

This story contains tropes such as:

Season 1

• Action Prologue: The first chapter is a prologue of sorts for the main plot, and a decent chunk of it is dedicated to a fight between Chara and Sans in a previous loop.
• Adaptational Badass: Sans' preparation for Chara's inevitable appearance mostly involves making the stronger monsters before him much more of a problem, so this trope is a given.
  • Sans himself now possesses determination (the aspect of the soul, not the personality trait). Not only that, but he possesses it naturally, like Undyne, and it comes with a nifty Healing Factor and general boost to his durability. He also becomes a lot more clever with his bones and Gaster Blasters, generating various skeletal constructs to improve his options in battle. He also manifests something of a precursor to his own version of Undyne's Undying form, though is unable to go all the way with the transformation just yet.
  • Toriel is far less rusty combat-wise than she was in the original game, and even surpassed her original skills in fire magic, allowing for things such as flaming Sword Beams from her fingertips, burning threads, and even a heat haze mirage to take her place and distract the opponent.
  • Papyrus learns to manifest a glowing eye akin to Sans, makes using his own Gaster Blasters significantly more convenient, and develops a brand new fighting style based in equipping his Blasters to his gloves and boots.
  • Undyne is able to handle her determination a decent bit better now, allowing her to use her Undying form with far less strain. She even manages to utilize sorcery in a version of her True Hero form, though that's a little zigzagged with Adaptational Wimp.
  • Mettaton NEO can actually fight due to all of his combat functions being fully reintegrated, showing off his extremely powerful arsenal and near-limitless stamina.
  • Even Chara is this, despite being completely out of the loop when it comes to Sans' preparation effort. It is confirmed that they are now a demon instead of a human, which comes equipped with full control of the hate within their soul. And that's hate in the Glitchtale sense, so you might be able to see the problem. Not to mention the Immeasurable LOVE state, in which the world simply gives up on calculating their total LV and causes anything they strike to simply be rendered "dead" regardless of durability or defense.
    • And in a comparison to Dusttale, the number of resets that Chara had gone through is at least portrayed as significantly higher. While Dusttale gives an exact number (327 by the time the game starts), UnderVow keeps it to large, yet vague terms such as "countless".
• Adaptational Context Change:
  • Chara's rise to their current power is different compared to Dusttale. While the Dusttale version of Chara grew as powerful as they did due to Frisk giving up their soul hundreds of times over (something that is impossible to do, as Chara only takes your soul once and then restores the world for free every subsequent time), the UnderVow version avoids the resulting Plot Hole via a demonic transformation after gaining a metric shit-ton of total LV over the many resets.
  • On Glitchtale's end, there's how exactly Chara got the hate that allowed their demonization to occur. In Glitchtale, it's because Frisk dumped it onto them after the aborted genocide run. Here, the first genocide run was not aborted, meaning Frisk gave Chara their soul... along with all the hate it had built up over the genocide.
• Adaptational Wimp: Despite the plentiful amount of Adaptational Badass, there are also some nerfs to things in this story.
  • Monsters as a whole have received a major limit as to how much magic they can use. While humans generally only become somewhat exhausted after overusing their magic, that's because they're mostly physical matter. As in Undertale proper, monsters are mostly comprised of magical energy; here, that's contextualized as monsters who use too much magic being unable to maintain what little physicality they have and consequently dusting themselves. This phenomenon is known In-Universe as "burning out".
  • On that topic, Undyne's True Hero form is almost completely recontextualized compared to its origins in Glitchtale. While still the result of a massive boost in determination, the difference is that Undyne had burned herself out by the time it occured. Because of this, rather than being a pure Next Tier Power-Up with no real drawbacks aside from a time limit, it is the transformation equivalent of a Death or Glory Attack, her form being held together by nothing but determination. The only explicit "advantages" are her becoming The Juggernaut and her spears changing from magic to sorcery.
• Adaptation Expansion:
  • The whole system of magic has been expanded upon, even aside from inclusion of concepts from Glitchtale. Here, "magic" mainly refers to what the monsters tend to use in-game, and draws from the magical energy within the user's body. Meanwhile, soul-based magic like what is shown in Glitchtale is referred to as "sorcery" instead. Monsters have stronger (if riskier due to burnout) magic due to larger amounts of magical energy, humans have stronger sorcery due to stronger souls.
  • On that note, hate has been given some expansion as well, compared to its appearance in Glitchtale. Along with all the applications and methods of manipulation shown there, it is possible (if extraordinarily difficult) to perfectly meld the hate with the user's soul, resulting in them becoming something known as a "demon". Demons can be either humans or monsters, but are generally The Dreaded due to their power and (typically) malice. Understandable, given how all of hate's benefits are retained while the drawbacks are minimized.
  • The story also expands on both Sans' Karmic Retribution ability and the rainbow-colored SAVE button from the Final Boss battle of the True Pacifist Route. The former is specified to grow stronger the higher the opponent's LV, while the latter is specified to function by tracing the connections between people's souls, then pulling them out of whatever nonsense they're caught up in by using said connections.
• Affectionate Nickname: Chara has a tendency to dole these out. For example, Sans is called "Sansy", and Flowey (aka Asriel) is known as "Azzy".
• Ambiguous Gender: Unlike one of its inspirations, UnderVow seems to be keeping Frisk and Chara's genders undefined, with both being referred to by gender-neutral terms and pronouns.
• An Aesop: By the author's own admission, "curiosity killed the cat". Just because you want to know what happens if you do something, you shouldn't do it. Otherwise, you might end up wishing you never even thought about it.
• Anti-Magic: The fight against the two Royal Guards in Hotland introduces the concept of reverse sorcery runes. When engraved onto an object, that object can assimilate part of any sorcery thrown at it, and then recreate an equal and opposite frequency to cancel out the rest.
• Armor-Piercing Attack: Chara's attacks in their Immeasurable LOVE state are stated by Mettaton to ignore the target's defenses.
• Awesome, but Impractical: The reverse sorcery runes mentioned above are certainly powerful, what with shutting down a lot of humanity's offensive potential... but something as simple as the fur of the dog unit is enough to mess them up and render them useless.
• Bare-Fisted Monk: Frisk simply fights with enhanced punches and kicks, likely because a stick isn't the best weapon.
• Battle in the Center of the Mind: Frisk ends up forcing Chara to miss all of their attempts at finishing Sans off, culminating in them ending up stabbing themselves. This leads into an internal battle between the two humans.
• Blood Knight: Not too pronounced, but it is repeatedly shown that all the time dealing in murderous resets caused Chara to genuinely get a thrill out of a proper fight. They would always look forward to Undyne the Undying and Sans, and the multiple levels of badass taken by this timeline in particular cause them no shortage of excitement.
• Character Catchphrase: Whenever somebody questions how Sans seems to know so much, he responds with "I have my ways/reasons".
• Combat Pragmatist: Even though they'd much rather have a straightforward fight, Chara is far from being above being tricky. For example, when fighting against The Juggernaut that is True Hero Undyne, after realizing that any damage they can dish out may just be insignificant as is, they lure her into Hotland to make use of the weakness to its extreme heat that Undyne displayed in more pacifistic timelines, before cutting down the bridge and letting her fall into the lava.
• Crazy Enough to Work: The rainbow SAVE button was not meant to be used on one's self, but Frisk does so anyway to try and end their fight against Chara. It ends up working, causing them to share Frisk's soul (before they split it up, anyway) and pull both themselves and Sans into the save room.

• Dirty Coward: Surprisingly enough, Flowey is depicted as this. After so many resets and so much torment by Chara, he has essentially given up on trying to fight back against the demon, and lambasts Sans for even suggesting it due to how impossible he perceives it as.
• Faux Affably Evil: Chara may be a genocidal demon, but they are also an absolute dork with a proper sense of humor not drenched in Black Comedy. They are not above slaughtering all in their way, just like they're not above making "cool" and "cute" poses in the mirror or purposefully making Papyrus as uncomfortable as possible after facetanking the electric maze.
• Healing Factor:
  • Word of God states that determination, while it does melt monsters down when they grow too weak, also does its best to keep them together. This is the writer's explanation towards why Undyne could remain in action for several turns before dying if killed in a neutral route, and it also makes Sans much harder to kill if his soul isn't struck directly, as any parts of him that get broken or sliced off will simply melt down and meld back with his body to reform.
  • Hate users (and, by extension, demons) are also able to regenerate their wounds through said hate, it perfectly replacing any lost tissue. More severe wounds take more time and effort to heal, but it's safe to say that physical damage alone likely isn't enough to strike a demon down.
• Humanoid Abomination: As implied by Flowey and later confirmed by Gaster, Chara is no longer what one would normally consider human. Instead, they are a demon: an entity that has fully internalized and merged with hate through extremely difficult means (like Chara's absurd total sum of LV) to become a being beyond standard humans and monsters, gaining all the benefits of hate with none of the drawbacks. It is shown off perfectly in their occasional Black Eyes of Crazy, as well as after getting severely damaged by Papyrus and Undyne, being surrounded in a black aura so thick that they barely look human at all as the hate goes into overdrive to regenerate them. Then there's their Immeasurable LOVE state, where they draw upon the typically-inaccessible well of LV they have built up over the loops, which, for them, is so ridiculously high that the world simply gave up on calculating it. Anything they strike with it active is immediately rendered as "dead" regardless of HP or defense, and even lets them kill things without conventional HP (at least if put in game terms).
• Kung-Fu Wizard: Papyrus' final fighting style involves him equipping his Gaster Blasters on his arms and legs, allowing him to augment his punches and kicks with beams and bursts of energy and release various energy attacks via martial arts.
• Our Demons Are Different: Here, they are either humans or monsters that have managed to fully assimilate and fuse their soul with hate in a way distinct from trait inversion. This grants them all the benefits of hate while minimizing the drawbacks. Demons as a whole are essentially boogeymen to any that know of them.
• Painting the Medium: Somewhat. Every mention of hate (the soul trait) in the story is written in bold letters, putting emphasis on when it's the trait or the emotion being talked about.
• Power Dyes Your Hair: An overload of determination apparently causes Frisk's hair to turn a faintly glowing red.
• Razor Wings: Apparently, Mettaton NEO's wings are able to function as sharp piercing blades.
• Ripple-Effect-Proof Memory: Some select characters possess it, namely being Chara (as the one behind the ripple effect in question), Flowey, and (at least in this timeline) Sans. However, it seems that simply possessing large amounts of determination isn't enough to remember, as Chara specifically points out Undyne's lack of this trope while interrogating Flowey at the end of the Ruins.
• Sequel Hook: Frisk breaks the endless genocide loop, and then goes through their "last pacifist run": the final run through the underground which ends in the best ending, which they remain in for good. All the monsters are free, and Sans is at relative peace... but someone then captures the now free sextet of human souls for some sort of mysterious plan. Word of God even states that this is a teaser towards season 2.
• Shout-Out:
  • As confirmed by Word of God, True Hero Undyne being referred to as "a being called Undyne" was intended to be a reference to Digimon Story: Cyber Sleuth.
  • In the story itself, several anime series are referenced by name in the general context of Alphys, such as Tokyo Revengers and Bleach.
• The Power of Hate: Coming straight out of Glitchtale, hate is a soul trait of sorts that enhances basically all of the host's abilities at the cost of sapping away their personality and sense of self, until they become nothing more than an Empty Shell for it to use as it pleases. The removal of that drawback is why demons are so feared.
• Took a Level in Badass: Every single important character. Not even joking, all of the main monsters have received buffs in this story, with the sole exceptions of Asgore and Flowey (though he isn't really a monster). Even Chara has become a true demon as far as this setting is concerned, gaining a significant upgrade to their abilities.
• Well-Intentioned Extremist: Frisk, at least after the first genocide run. They went through a soulless pacifist run, hated the genocide repeat it ended in, and then decided to do as many subsequent genocides as necessary to get their soul back, as they only met directly at the end of such. After that, they would reset again and go through the true pacifist run again, the ending of which they would keep around for good.

To Render A World Unresponsive

• All Your Powers Combined: Tenacity!Sans is rather explicitly able to utilize and combine any and all of Sans and Chara's respective abilities, including even Karmic Retribution and Immeasurable LOVE.
• Bash Brothers: Sans still doesn't like Chara, and Chara loves to screw with Sans. Even with that in mind, they are more than capable to fighting against Error.
• Body Horror: Error sustains some pretty gruesome damage during his fight with Sans and Chara, and at one point, his Sans-esque mouth actually opens up due to all the stress inflicted upon him, which is extremely unsettling to say the least. Thank god for that Healing Factor...
• The Cameo: Ink and Fresh show up at the end of the story.
• Dimensional Traveler: Error, as per usual, is traveling through Alternate Universes to destroy them. He even pulls Sans and Chara into the Anti-Void at one point.
• Fusion Dance: Desperate to break free of Error's strings and stop him from destroying their world, Sans and Chara resort to having Sans absorb Chara's demonized soul. Due to the fact that Chara doesn't really have proper physical body at this point, this results in Chara being completely assimilated into Sans' form, resulting in a brand new entity that the writer refers to as Tenacity!Sans, or just Tenacity for short.
• Genius Bruiser: Sans, as per usual, but Tenacity is an even greater example, as he's a full-blown Lightning Bruiser with several unique abilities as opposed to the mostly still Fragile Speedster Glass Cannon carried by special abilities that is Sans.
• Guardian Entity: Chara acts as something akin to this for Frisk, coming out when Frisk is captured by Error and then proceeding to try and fight alongside Frisk. This doesn't work out too well, and leads into them fighting alongside Sans instead.
• Healing Factor: It appears that Error has this via glitching himself back to prime condition. During Tenacity's fight, it's revealed to be a bit more complicated, in that Error's constantly fluctuating stats sometimes result in Maximum HP Reduction down to less than his remaining HP, resulting in him going back to full.
• Hour of Power: Technically. Tenacity is very strong, but he was mainly useful due to the fight occuring in the Anti-Void^note outside of any particular universe. This is because, as ridiculously overpowered as he is, his existence is a similar "distortion" to Chara's Immeasurable LOVE state. As the world doesn't like such distortions, the moment that Tenacity went back to the UnderVow world, he was quickly forced back apart.
• Loose Canon: Done entirely on purpose. Technically speaking, this story is not canon to UnderVow proper. However, things like the creation of Tenacity!Sans are very much possible in canon, and Word of God is that any big inter-AU crossover is free to treat the story as canonical if so desired.
• Not Quite Dead: Error pulls this twice against Sans and Chara.
  • The first time is after Sans blasted him point-blank with a full-power fission beam from his Blast Dragon into the ground, leaving a deep crater that Error couldn't be seen in and which then repaired itself due to Anti-Void shenanigans. He proceeded to break out of the ground, more heavily injured than ever before, and wrap up Sans and Chara so they stop getting in his way.
  • The second time is when in the subsequent fight, Tenacity launched an Immeasurable LOVE attack towards Error, with the glitchy skeleton being nowhere to be seen after the ensuing explosion. Turns out he had simply escaped into the Doodlesphere. Somewhat downplayed in that Tenacity immediately entertains the idea that he likely isn't dead.
• Worf Had the Flu: Upon manifesting, Tenacity proceeds to absolutely dogwalk Error, breaking down the nature of his apparent Healing Factor and immediately proceeding to make himself appear invincible. However, it's rather blatantly stated that Tenacity was an Outside-Context Problem for Error due to none of the records on the UnderVow timeline ever mentioning Sans and Chara performing a Fusion Dance like this, resulting in him being woefully unprepared.

Season 2

• Barbarian Long Hair: Typically, Akito Kuonji keeps his hair in an extremely long ponytail. But when the Emperor comes out against Frisk, it comes loose, fully evoking this trope.
• The Berserker: Unlike with Frisk, who is generally able to control themselves when powered up, Akito is... less successful. When pushed to the point of engaging his soul's full potential, he goes into a near-animalistic rampage. It's to the point where he isn't even referred to by name while in that state, only by his title of "the Emperor".
• Gladiator Games: The Soul Shatter Tournament is a monthly tournament designed specifically for magic and/or sorcery users. While the goal is to simply make the opponent give up or knock them out, outright killing them for a win is not exactly considered illegal. Frisk, on their end, sees the whole thing as the Blood Sport that it is and thinks it's stupid, even without its manager Mr. Benedict's attempts to bring monsters into it.
• Martial Pacifist: Frisk generally takes this sort of role after reaching the surface. While they most certainly have a "no killing" policy that they will abide by, they're not at all afraid of beating the shit out of someone until they concede.
• Red Baron: Akito Kuonji is also known as "the Emperor".
• Shout-Out:
  • The entire premise of the first/prologue chapter was inspired by Kengan Ashura, with Akito Kuonji being roughly based off of Kanoh Agito from that series.
  • The tournament the aformentioned chapter takes place in, the Soul Shatter Tournament, is named after a popular Undertale Player Versus Player fangame called Undertale: SoulShatters
• Super Mode: Turns out, Frisk's hair going red when they get especially determined isn't just a thing for them. It's actually a state any human can enter, in which not just their eyes, but their hair becomes the color of their soul. In this state, the potential of their soul (and thus their sorcery) is maximized, allowing for far greater combat power. The problem is, not everyone can remain in control of themselves when this state is active. Just ask Akito.
• Well-Intentioned Extremist: Frisk keeps the ball rolling with this trope in their role as ambassador, as they are shown to be willing to go quite the lengths to make sure the monsters are safe and happy amongst humans. The moment that the Soul Shatter Tournament starts trying to bring monsters into the fold, Frisk's first reaction is to try and cancel the whole thing permanently. In general, they're willing to do everything short of murder (accidental or not) for the sake of the monsters, and even that restriction is solely due to a vow of relative pacifism they made for this timeline.

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