Meru lets out a faint "thank you" for her classmates because they don't forget her even though she (temporarily) loses her quirk at chapter 289.
Every single of Nozomu's students waiting outside of his operation room after he was hit by a traincar.
Kafuka donated organs saving the girls from their Death by Despair and their gradual acceptance of each other as friends.
A single page at the end of several chapters that depicting Chiri and Harumi's childhood flashback are nothing but moments of heartwarming incarnates. There's a reason why these completely different girls that not necessarily understand each other's taste can be friends, after all.
Harumi, seeing that Chiri playing chutes and ladders alone (with three imaginary friends), offers to play with her because she thinks it's so lonely to be alone.
Chiri driving off a Lolicon from kidnapping Harumi with a shovel while adults in vicinity don't giving a damn.
Playing mock "Freaky Friday" Flip, Harumi proceeds to act in-character by cleaning their entire neighborhood. Chiri (blushingly) denies that she's that nice of a little girl.
Chiri at first didn't want to make friends because she knew that she might move again one day due to her father's job. Harumi tricks her by becoming rivals at random challenges and vow that even if they can't be friends, they will always be rivals and will see each other again to finish their rivalry. Unfortunately, this backfires as they never really declared their friendship after they find out that Chiri's family decided to settle down in that city.
Around chapter 150-165-ish, Kafuka, Nozomu and Chie decide to ride the mystery train together. During their trip, Kafuka asks Nozomu if he's decided on who he's going to marry. He then gives a slight smile and blushes, simply saying "yes". Kafuka later decides to put off losing her virginity. It's a long story.