In episode 6, Chloe tells Ao about her plan to defeat the G-Monster by fighting it inside the ZOA, which failed horribly when they discovered it could regenerate. She's on the verge of tears since she made the plan just to show that Ao wasn't the only person capable of such close-range fighting. Getting an idea, Ao decides to go out and prove she was right, echoing (now dead) Bruno's line about hurting those close to you.
Also, Chief Bruno himself is a walking personification of heartwarming. He basically acts like a second father to the girls of Goldilocks and is one of the nicest guys you can ever meet. He even shares Ivica's dedication to never wanting to let children die.
After the events of episode 11, the first thing Ivica does is hug both Ao and Elena to make sure they're both all right.
Ao getting to see his mother in episode 12, even if it is somewhat awkward that she's still pregnant with him.
All of Ao and Eureka's interactions. She may not technically be his mom yet, but she acts like it. Then there's her somewhat unflattering description of Renton, yet she loves him all the same.
Endo comes off as a My Country, Right or Wrong guy at first, barging in and taking Eureka under cover of gunfire to manipulate her, but when push comes to shove he does the right thing, protecting her and her kid. He made a promise, and he delivers, even if was kind of like throwing rocks at a giant.
Lt. Nakamura pulls a gun on Ao, so literally every other person present makes a move to not let that happen.
In a role-reversal of episode 6, Chloe ends up staying by Ao's bedside after he gets shot down by a Secret.
Episode 18 shows just how much the kids treasure each other.
Episode 19 shows that, for all their faults, Fleur and her father know each other very well.
Naru still cares deeply about Ao and even tricked Truth into helping Ao gain the Cannon.
Fleur crying when Elena leaves in Episode 20, showing how much she considers her a friend.
Ao convincing Elena to come back in episode 21, by telling her that she and all their friends are his family.
Naru saving Ao in episode 22, finally setting the record straight about her and Truth, and saying that she wants to spend the rest of her life with Ao and grow old together with him. Then episode 23 happened.
Naru actually does make a Heel–Face Turn in the manga adaptation, even getting to become besties with Fleur and Elena.
The Grand Finale's last scene. Ao finally ends up returning home after years of limbo and Truth assuming that his friends and family will have forgotten him. But then Fleur and Elena RECOGNIZE him. Truth is heard remarking, "Perhaps I was wrong after all.", and flies off into the great beyond. Ao is overcome with relief and bawls a mountain of tears.