Little Nic apologizing to Worick in a flashback chapter. Thanks to his then limited grasp of speaking, he actually says "Sowwy."
Just about every flashback focusing on young Worick and Nick, really, from Worick teaching Nic his letters to Nic turning back around, with a sudden memory of Worick having given him his book of sign language, as soon as he sees the book fall just to grab at it, even in the incredibly dangerous situation he's in only for him to wind up right in the range of a grenade. The heartwarming moments are subtler when they're older, but they still shine every once in a while, like when Worick almost attacks an unarmed woman when she starts insulting Nic horribly by a brothel, only to be stopped by Nic; later he thinks to himself that he'd rather deny that he cares about Nic and other Twilights, but it's obvious that he does.
Nic and Alex's relationship quickly becomes this in later chapters, starting with his short, in-between-the-lines, spoken acknowledgement of her learning from the sign language book (which, as we learn later, was very precious to him as a kid, and probably still is) after she tries to speak to him with it, to his defending her in his own way when a woman questions him about her, to his sudden, furious appearance right as she's in danger to drive back men who come after her (contrasting when he'd done something alike to it in the past, but didn't show as much emotion), to his giving her a Cooldown Hug when she's about to have a break down because of her withdrawal from Psycho Serum bringing back memories of family she's horrified to have forgotten, to her thanking him for protecting her earlier, asking if she could stay just a while longer since she couldn't find another place right now, only for him to reply out loud that her sign language was really messy, and that she needed to keep working on it so he could understand her.
Worick and Alex have an incredibly touching hug after he wakes up from a dark, memory-laden nightmare, with Alex telling him that she remembered her mother used to hold her like this when she was a child, whenever she was afraid. Worick also backs up Nic's indirect way of telling Alex that she could stay as long as she needed, to which she nearly looks like she's about to cry. Really, the Benriya three have a lot of moments between them like this, past or present.
Nic holding onto the twelve-year-old Nina while doing great, leaping spins through the air as she laughed with joy was very sweet as well.
Nic and Nina's relationship is just a ball of heartwarming. Nic giving Nina a drink when she shows up at their home, and Nina holding his hand when he's recovering in the clinic. Nina telling Alex that Nic is a good guy with a sweet smile on her face really sells it. They hold hands while walking down the street for crying out loud.