Heartwarming / Isekai Quartet

General

• Naofumi laughs and smiles a lot in this series, not having the stress of the Waves or being around the Idiot Trio, while at the same time being with his True Companions seems to have taken a huge weight off his shoulders. This is likely the closest Shield Hero fans will get to see of him as he was before his story began.

Season 1

Opening/Ending

• While the opening is a hilarious introduction to the story, it's also about the four main characters (Ainz, Kazuma, Subaru, and Tanya) acknowledging that, even if they want to go back home, the new world they are in is quite good and it makes them feel welcome.
• Out of context, the ending just sounds like a cheerful catchy little number by some of the main female protagonists of their respective universes, but when you learn it's basically the girls talking about having a "girl's night out" and singing about how much they look forward to enjoying it, it becomes many levels of adorable.

Episode 1: Come Together! Quartet

• After the Re:Zero casts see how scary looking their new classmates are, Rem vows to protect Subaru and Emilia. Emilia, as well, expressing her desire to make friends with them.

Episode 3: Deadlock! Classmates

• Albedo instantly bonding with Rem over their belief in Love at First Sight is an oddly sweet (and hilarious) Pet the Dog moment, considering her usual attitude toward humans.

Episode 4: Encounter! Classmates

• This episode has Ainz and Tanya, the vilest beings in the Isekai multiverse, actually befriending one another. It goes to show that deep down, they haven't lost their humanity.
  • This is also a big step up for Tanya. She might have been hesitant to trust anyone, let alone a salaryman considering her origin story.
• Also, before Kazuma lets his jealousy get the best of him, Subaru and he manage to connect through their shared experiences as fellow isekai deconstructions.

Episode 5: Explosion! Talent Show

• Remembering his own boring talent show when he was a salaryman, Ainz recalls the moment that made all his co-workers excited: when they went outside to find it was snowing. So to end the talent show, he uses a Super-Tier magic spell to fill the sky with clouds and have it snow, to the merriment of the other groups.
  • The song that plays during the snowfall emphasizes how heartwarming that moment was.
  • Ainz's very choice of the spell might be another layer of heartwarming as well. Sure, he could probably just cast a way more powerful explosion type spell, but he went a different route. He might have picked a different spell, just so that Megumin wouldn't lose any applause for her level of Explosion magic.
  • It's even more heartwarming and even a bit of a Tear Jerker when one remembers that Ainz's world is a Crapsack World, with the environment destroyed by overpopulation, wars, and pollution. Seeing snow must be an incredibly rare event for people there, which is what makes Ainz choosing to make it snow so special; he could very well consider it a precious event and give so much meaning to something we take a bit for granted.

Episode 7: Carry Out! Class Rep

• Emilia sitting with Puck talking about how, even if it gets difficult she plans to work hard in her new role as Class Rep. Her smile and the fun she is having, when looking back on her home series is incredibly heartwarming because here she is more or less a normal girl and able to enjoy the life of a high school student.
• Subaru mentions offhandedly how Hamsuke likes to chew on his head to Rem and she immediately decides to take Hamsuke down: no matter the world, you do not mess with Subaru when she is around.
• Beatrice's assertion that she is not making friends with Mare comes under immediate suspicion after she runs after Mare to help open the library.

Episode 8: Prepare! Field Trip

• Aqua shockingly defending Albedo against Shalltear for being a virgin. While she might dislike Albedo for being a demon, she draws the line at mocking people for doing what they want to do.
  • What makes it doubly heartwarming is that Aqua genuinely believes that too, as she was defending Albedo using the Axis Cult's creed since it's literally one of her rules for her faith's believers.

Episode 9: Enjoy! Field Trip

• When Tanya erupts in fury upon assuming that Aqua is Being X and looks ready to murder her, Subaru and Ainz both defend Aqua, with Subaru stepping DIRECTLY between Aqua and the enraged Tanya, while Ainz talks Tanya down with reason (especially notable since Aqua had actually tried to kill Ainz herself back in episode 2). For her part, Tanya sincerely apologizes for nearly attacking Aqua once she calms down.

Episode 10: Join in! Rivals

• In this episode, Subaru, Ainz, and Tanya formed a meeting and discuss how they're going to win and get back home. You can tell that the three have become close friends.
• And they are not the only ones. Rem is having lunch with Albedo and Shalltear.
• Chris, as usual, has to hear Aqua badmouthing her secret identity. She would have taken it with ease, but then she clenches her fist. Why? Because Aqua was talking back at Darkness. She can take the insults, but never insult her followers especially her best friend.
• When Subaru wishes to help everyone get back, Ram and Beatrice, of all people, support that notion. It goes to show that they do care for the young teen.

Episode 11: Work Together! Field Day

• As Megumin taunts Yunyun for being the only member of Class 3 and having no friends, Cocytus defends Yunyun by telling Megumin to shut up.

Episode 12: Band Together! Quartet

• When Kazuma uses Steal to make the Destroyer fall over as one of its legs falls off, Tanya is legitimately impressed and acknowledges him, going so far as to say that if they were in her world, he would have been conscripted for his usefulness. Considering how Tanya is in her original world, this says a lot.
• During the fight with the Destroyer, after a great Bad Ass Boast, Subaru puts himself at risk when he tosses Tanya and Kazuma out of the way of the Destroyer, encouraging them as he falls, while Emilia can't help but worry. Rem, however, who has seen Subaru take down the White Whale, offers reassurance that Subaru will be just fine. He then weaponizes Return by Death again to use Ainz's Undeath Army^note Which he only recently learned worked on Undead as well as Mabeasts to protect the others from the Destroyer's beam attack.

Season 2

Opening/Ending

• The ending is all sorts of adorable when you take a look at the lyrics, and realize that the entire song is simply about the secondary heroines of their respective series getting excited because it's now their turn to shine on stage.

Episode 13: Join the Fight! Transfer Student

• Wilhelm invites a wandering Naofumi to have a drink and tells him that maybe he's in this new world for a reason. Naofumi doesn't overreact, and his only worry is to find Raphtalia and Filo.
  • Re:Zero faithfuls will notice a bouquet of yellow flowers on Wilhelm's table. These flowers in particular are the favorite of his late wife Theresia van Astrea.
• When Raphtalia finds Ainz in the school, she gets ready to attack, but Kazuma halts her, and he and Ainz offer to help her find Naofumi.
• Filo has fun giving Mare and Subaru a ride around in her Filolial form, and when Raphtalia arrives, she transforms into her humanoid form and immediately runs to hug her. Kazuma is glad that Raphtalia has found one of her friends, and Aura comments on how cool Filo is.
• After saving them from being hit by the baseball, Naofumi immediately checks that Raphtalia and Filo are alright, and tells them that he's glad they are still together.
  • Also, notice that he smiles - something that is made more powerful by the fact that he had few reasons to do it in his own series.
• An understated example but, throughout the episode, we see the characters playing and chatting with each other naturally, showing how they bonded in Season 1.

Episode 15: Uh-Oh! Detention!

• To get Kazuma, Aqua, Grantz, Koenig, and Neumann out of detention, Rerugen explains to Subaru and Emilia that the five in question must perform a good deed, with Megumin having a plan to get them out. Emilia being genuinely delighted that there is a way to help out her classmates is shown to visibly move Rerugen, with him even remarking on how much of an angel she is.
• In science class, everyone in the class minus Tanya is in on the plan to get their classmates' detention reduced, with Visha and Weiss both helping Megumin put it into action^note Her plan is to set off a contained explosion and blow up a bunsen burner, which ends up also triggering a flood.
  • When Tanya does find out what is happening, Ainz actually steps in and tells her to let them do what they want, as they are trying to help the others, despite her protests as the disciplinarian.
  • Though it may not seem so, Ram hints that even Roswaal is in on the plan as well.
• When Kazuma and co. bump into Principal Rudersdorf as the flood is happening, the latter requests their assistance to stop the flood, and in return, he'll end their detention, citing that good deeds must be awarded.

Episode 16: Pinch! Test of Learning!

• When Kazuma is warned by Grantz not to cheat, Megumin comes to his aid, and tells Tanya that Kazuma is smarter than he appears, and Tanya comments that maybe she misjudged him and apologizes for that. Kazuma's thoughts show he really was going to cheat, but that compliment is enough for him to take it honestly.

Episode 17: Work Hard! Valentine's Day!

• Though played for laughs, Megumin explains to Emilia and Visha that Kazuma (who explained to her the entire idea of Valentine's Day) has never experienced Valentine's Day once in his life and that the only chocolate that he'd receive is only from his mother. During the montage of characters receiving chocolate at the end of the episode, Aqua, Megumin, and Darkness all give him chocolate, and then in the next shot, we see Kazuma in the hallway, jumping in the air with joy, happy as he can be.
• Seeing Yunyun at the ending of the episode with her arms full of chocolate. Even if it's just a single still, it speaks volumes, showing that she's actually loved in this world.
• The gifts start in Wilhelm and Sebas Tian's tatami mat room. We see a black box with pink trim and gold ribbon, probably Sebas' that may represent Tuare, who was saved by and fell in love with him. The second is a white box with a dove carrying 3 flowers is probably Wilhelm's. This brings the moment into a tearjerker as the dove represents peace and the flowers were the same as the ones that bloomed when he met his wife Theresia, a Sword Saint who loved flowers and died fighting the White Whale, a monster on par with a natural disaster in Re:Zero.
• We also get to see Ram give Roswaal chocolate, complete with a genuine smile on her face.
• One can only imagine the look on Rerugen's face when Tanya offers him some chocolate!
• Turning the tradition on its head, Naofumi gives Raphtalia and Filo chocolate, with their happiness giving him the brightest smile we will likely ever see out of the character.

Episode 18: Clash! Dodgeball!

• Visha squeeing about how good the karaage at a butcher shop is, when you remember the war-torn world that she comes from and the fact that Tanya hates German-style cuisine, it's nice to see them get worked up over the little things.
• When the class breaks up into Salt and Pepper, Ketchup, and Mayonnaise, Cocytus is the only one to pick Salt and Pepper, while most of the Overlord cast sided with Ainz and ketchup. When the camera focuses on him, he is reminding himself that he is still loyal under his breath, while Ainz just accepts it.
• The fact that Rerugen just goes with this whole argument shows how much he's relaxed in this world, in great contrast in the world where he, Tanya, and the rest of the Youjo Senki characters hail from.
• Naofumi wants no part of the dodgeball game, the only reason he sticks around is that Filo thinks it would be fun.
  • Raphtalia is very regretful about being put on a different team, but Naofumi just laughs and says ketchup suits her.
• Even in this other world, Beatrice remembers her oath to protect Subaru and saves him from Chomesuke's flaming ball of death.
• The fact that Ainz and Tanya make up by the end of the episode. It's heartwarming, seeing that both of them, whom for sure are the least apologetic over anything they do, being able to show just a bit of humility and reconcile.

Episode 19: Excitment! Physicals Day!

• Overhearing from Subaru that he refuses to peek on the girls during their physicals, Julius briefly admires how much he has grown as a knight.
  • Cocytus^note he was the one who popped the question to Subaru also commends Subaru for following "the warrior's path."

Episode 20: Challenge! Part-Time Job!

• Although the reasoning for everyone else doing so is played for laughs, it's somewhat nice seeing that the entirety of Class 2 decided to get jobs just like Visha.
• Tanya being so kind to treat everyone to coffee to make up for her comrade's "silliness" is sweet, coming from her.

Episode 21: Investigate! First Errand!

• Naofumi shows none of the wariness that defines much of his characterization in his home series and is completely comfortable with letting Filo roam around the school to ask other students for ideas for the play - in fact, he actually encourages it, thinking this would be good for Filo. It certainly speaks volumes about how much he trusts the other students if he is willing to let Filo mingle with them, unlike the case with his home series.
• In a child-like way, it's adorable hearing Filo identifies the other characters, seeing she doesn't remember their names.
  • Ainz is called "Skeleton Man", "Skeleton Guy" and "Grandpa".
    • What is really great about Ainz's nickname is that he commends her for trying in his head.
  • Beatrice is called "Beako", just like Subaru does.
    • She even elicits the same response Beatrice gives to Subaru when he says it.
  • Lupusregina is called "The Wolf Girl"
• After going to Kazuma and Tanya to get advice about the story and getting nowhere, Visha gives Filo a treat and asks her if it's good.
• As compared to everyone she meets in this episode, Emilia is probably the nicest to Filo, treating her more like an actual child than anybody so far. She watches what she says, speaks at a level Filo is sure to understand, and actually listens to her troubles, all while leaning down to keep eye-contact with her while giving her advice and waving good-bye. Seriously, Emilia is such a good girl.
• Though whether what they did could be considered helping or not, it's sweet that the Pleiades that were present in this scene were willing to help Filo find a story to do a play on.
• The fact that no one is mean to Filo, or treats her in any negative way, including Narberal Gamma, the same girl who hates anyone and everyone not originating from Nazarick and is one of the two most dangerous of the Pleiades. Not even she is disrespectful or mean to her, but rather treats her with respect. In fact, the only one who doesn't have a nice thing to say about her after is Beatrice.

Episode 23: It Begins! School Festival!

• When the Destroyer returns to the school, Tanya immediately wants to go and stop it, with Kazuma, Ainz, and Subaru following suit alongside Naofumi, Julius, and Reinhard. However, Roswaal stops them because their plays are starting, and asks if there's no one else they can rely upon besides themselves. That's when the group realizes that their companions are willing to fight in their stead. It just goes to show how much trust they have in one another.
• Ainz throughout the episode is the most human he's been in a long while, being friendly competitive with Julius and Reinhard, bantering with Tanya, asking that people pay attention to his real face and not the horse head and wondering why Tanya, Kazuma, and Subaru sympathize with Naofumi but not him.

Episode 24: The Show Begins! Showtime

• When Albedo saves Aqua, she repeats Aqua's words from episode 8 showing that she is grateful for Aqua's words.