WARNING: Per wiki policy, spoilers are off on Heartwarming pages.
Events
In one of the dating events with Scott, he runs to you saying that he's been thinking about how much he likes you and wants to share his favorite things with you to reflect that. And that the best place to start would be cheerleading, since you're not on the football team with him. You can suggest that you cheer for "each other, because friendship is the greatest sport of all", and if you pass the CHARM check, the cheering that ensues leads to the two of you repeatedly tossing each other into the air until the two of you wind up in space.
Scott: I can't tell if this burning in my heart is me getting burned up by the sun, or my love for you!
Both of Zoe's secret endings in Second Term qualify as this, as both have notable allegories to transgender identity, and the struggles people go through during gender transitions to be accepted by those around them:
In one, her change from Z'Gord into Zoe has been met with positive support by the majority of the student body, and Vera and Damien are quick to (violently) defend her whenever a jackass refuses to stop calling her Z'Gord. Even the Wolfpack attempt to respect Zoe's new identity, even though they don't understand the reasoning behind it.
In the other, her bumbling cultists are earnestly trying to get used to communing with their "Dread Mistress" Zoe instead of their old god Z'Gord in the manner of underinformed but doting family members learning how to best show support for a relative who's just come out of the closet (with a wacky Lovecraftian twist).
Dates
Getting Liam to go to the prom is oddly sweet. He drops the act of trying to act cool and enjoys the party, and different than various other endings, there isn't anything particularly crazy about, and it's just a sweet date between him and the player.
The prom date with Scott is also quite cute, in one of them, you'll learn more about him and that he likes the stars and the sky, which, is oddly sweet.
In an oddly sweet moment for Vera, she is a lovely date, and even says goodbye to you with a kiss on the cheek.
If you make the right choices while courting Polly, she'll call you her favorite party favor besides meth.
Secret Endings
The PROM KING ending. Liam accepts all the cliched tropes he is living through and is crying Tears of Joy from being elected. He even admits having fallen for the player through this.
The POLLY'S PARTY ending. After spending so long trying to determine the formula for the "perfect party" and indulging in your findings at prom, you and Polly end up watching the sunrise as she says, rather gently, that she thinks the formula to a perfect party is "sharing it with the right people" as you two hold hands.
The SEASON FINALE ending. You ask Joy of the Coven to prom. Hope and Faith tell her to go and enjoy herself while they handle the latest quest.
The HAIR ending. Damien opens up about his passion in wanting to be a hairdresser, and how he's worried about how his dads will take it. Fortunately, his dads are understanding.
Even further, we get some backstory on how Damien's dads met: both were fighting to conquer the Eighth Circle of Hell and decide to form an alliance. As such, this is how the pair fell in love. As a result, love is seen as important in that particular circle.
The Christmas update adds several new endings, of which the DRAWING route deserves special mention. Scott reveals to you and Vera that he never knew his parents, and becomes preoccupied with identifying who they are. Culminating in him admitting that what seems like his usual ditzy behavior over the whole affair is kind of him just trying to cope with wanting to find them. This admission prompts Vera (who, having been an orphan, understands how he feels) and Coach to assure him that family doesn't need to be all about blood, and that family can be the ones a person cares about. The ending CG features Scott, Vera, Coach, and the Wolfpack all hanging out in a happy group... after a scene in which Scott calls Coach a surrogate dad and Vera informs Scott that "you remind me that life doesn't always need to be hell, and that people don't always need to be shitty".
The Gift Update adds a new item to the Gift Box: A coupon for a date with Valerie. Throughout the route, you and Valerie get gifts for Valerie's' classmates and friends, before you surprise her with a gift of her own. At the end of the route, Valerie redeems your coupon, with said date turning out to be her inviting you to dinner at the Oberlin household.
Though it definitely crosses over with Tear Jerker territory, the EEL ending qualifies as this. After Miranda's death, the usual Polaroids of the cast having fun is replaced with Polaroids of the cast at Miranda's funeral. All of them are clearly and openly grieving her death, with Polly in particular openly weeping while hugging Miranda's In Memoriam photo. Unlike most depictions of death in this game, Miranda's is played dead seriously. Despite her selfish nature and homicidal rule, she meant a lot to her friends, and they're devastated that she's gone.
The ICE QUEEN ending goes into Vera's backstory. From developing a friendship with Scott (the core love interest she arguably has the least in common with) after she learns he's an orphan, to being bullied and finding acceptance with her adoptive family, she's not as quite as ice-cold as she seems.
The SUPPORT GROUP Ending has Coach and Kale as apart of an asexual support group, due to the horny hijinks of the world. Its really nice to know that Asexuality and Aromanticism is represented in the game.
Though PRANK MASTERZ is a huge Downer Ending second only to EEL, there is something strangely heartwarming about Damien and Miranda's polaroid. It shows them leading their armies into battle together, in quite an uplifting display of teamwork and selflessness from the two of them (even if it is heavily implied to be a Bolivian Army Ending).
Polaroids
All the Polaroids, really, the entire ending theme. It's an Awesome Music over a montage of the main character being friends in a bunch of nice situations.
The personalized polaroids when you get a date, or secret ending are particularly cool, due to reaffirming your character's nature: an Adorkable high schooler with a big crush on their classmates.
Oz/Yellow's Polaroids:
His infatuation with Vera is very cute on a Polaroid in which he is excited about seeing her smile.
Oz: The world stops when she smiles...
His ending Polaroid with Zoe shows the two attending a convention dressed as Naruto and Garfield, respectively. It's especially sweet when you realize that they are couple cosplaying as Zoe's favorite ship.
Oz: Best ship EVER!!
Vicky/Blue's Polaroids:
In hers with Miranda, she is in the play, playing a knight protecting Miranda that is playing a princess.
Vicky: Nobody touches my Miri! I protec!
With Scott, she is in the background of a fair, giving a tail-wiggling happy Scott a giant teddy bear.
Vicky: My Furry Cutie-Patootie!
Second Term gives the two a unique Polaroid, in which they are out on a beach date and very clearly enjoying their time together. The caption above is kept for good measure.
With Vera, she offers the gorgon an umbrella on a rainy day.
Vicky: No day feels rainy w/ you.
Her new Polaroid with Damien sees the demon showcasing his rare soft side as he does Vicky's makeup.
Vicky: With you, everything is more beautiful.
Amira/Red's Polaroids:
Her special Polaroid with Scott, in which they are stargazing together with Amira wearing Scott's jacket.
Amira: The STAR of my nights!
Her Polaroid with Liam is of the gang playing a board game together - she's growling with frustration as he joyfully and dramatically makes a winning move against her, with his face circled by a heart.
Amira: FUCKING SEXY SMARTASS!
The updated version of the above displays Amira helping Liam with his posture during mini golf, which doesn't sound like much until you see that the latter is blushing from the former's proximity. Fittingly, the new caption is written as follows:
Amira: My purple dork. (Just tap it in)
Her Polaroid with Polly is an Adorkable moment of the ghost and Miranda playing in a pool, with Polly looking back at her and happily calling to her as she cowers in the distance wearing a towel. Remember, Amira is a fire genie.
Amira: Polly GOOD! Water BAD! (;_; I cry)
Second Term updates the above to the couple relaxing and laughing heartily together during a car trip.
Amira: Let's go nowhere together.
Brian/Green's Polaroids:
His special Polaroid with Liam, in which they are listening to music together on a bus.
Brian: No words needed.
Second Term gives Brian a Polaroid with Zoe featuring the two of them drawing together — specifically with an absolutely-smitten Zoe cranking out several pages of sketches of her new boyfriend while he comes up behind her to show her a doodle he's done of her and is impressed and flattered by her work.
Brian: I'm a fan of us.
His Second Term Polaroid with Vera sees the two of them walking side-by-side together on the grounds of a festival at night, dressed in yukata and smiling brightly at each other. If that wasn't adorable enough, especially considering the hard-hearted Vera, Brian's caption is downright sweet:
Brian: You are life to my afterlife.
His updated Polaroid with Scott displays the two after winning a football game, with Scott's arm wrapped around Brian and Brian carrying the winning trophy. What makes it better is this is one of the few Polaroids where Brian is full-on beaming with happiness.
Brian: Always have each others rears ;).
Monster Camp
Pretty much the entirety of the credits, which are animated this time around, and just depict everyone hanging out at camp and having a good time with each other. Especially Brian dozing off while Milo leans against him.
Successfully getting all the stat checks in Dahlia's Genie Flask storyline ends with the player character, Joy, Calculester, Aarvi and Damien rescuing Dahlia from Camp Rival Camp and Dimitri's machinations. Especially when Dahlia reaches a Heroic BSoD and Damien manages to snap her out of it and team up with to defeat Dimitri.
A new mechanic during nighttime campfire sessions is the Love Log, where if two players sit together, they both get stat boosts, as well as some adorable art of the PCs hanging out that borders on Ship Tease, such as Vicky and Amira sharing a blanket, Amira petting one of Oz's phobias, and so on.
Monster Roadtrip
Many of the choices that increase your SOUL end up being this.
Once again, the credits are full of sweet moments between the cast.
In one random event, you can chose to drink a love potion. Polly suggests blindfolding you and spinning you around so the person you see and fall in love with is random, since she thinks it'd be funny. But when you finally open your eyes, you're greeted with... a mirror. The group explains that they noticed your lack of self-confidence and thought you could use some self-love. And despite what you might think, it doesn't go full Narcissus, with the player simply indulging themself with a "date".
Other
The Steam Cards available with the "F*cking Hot Update" had some oddly sweet messages about the characters.
Rain: "Vicky Schmidt is upbeat and usually a nice, happy girl. But don't mistake her kindness for weakness: she's a huge overachiever with tons of willpower. She knows that she doesn't need to be mean or competitive to be strong."
Oz: "Oz appreciates loneliness from time to time. He's shy, and he sometimes feels pessimistic, but he likes surrounding himself with rather upbeat people. Doing so makes him happier and more positive, even if he highly appreciates people not directly pushing him to be that way."
Fair: "Scott Howl is the most loyal person in the world. He's always making efforts, trying to be the best version of himself and wants to help his friends do the same. Because of this, he's not only focused on sporting hard, but also on supporting everyone, sort of like a cheerleader."
Chat: "Vera loves money because she thinks being wealthy is a way of being free, and that way she doesn’t have to answer to anyone. Aside entrepreneurship, she enjoys voguing, a good single malt, and the Dark Arts. She's proud of being an Oberlin."
displays the two after winning a football game, with Scott's arm wrapped around Brian and Brian carrying the winning trophy. What makes it better is this is one of the few Polaroids where Brian is full-on beaming with happiness.Brian: Always have each others rears ;).