Heartwarming: Anti-Cliché and Mary-Sue Elimination Society
Michael being more than willing to sell his own soul to save Claire's life. That's true dedication to that relationship.
One of the biggest Heartwarming Moments has to be Michael proposing to Claire after a catastrophic attack from Alastor.
Tash and Adrian getting together - hell, Tash's initial confession.
Ben calming down and reassuring Lily.
Adrian and Aster exchanging final goodbyes.
Cristoph and Rhia's love for each other after Adrian's death.
Ossa and Aimee's acknowledging of each other.
Chrys greeting Aster from her coma.
Pretty much anything postmortem Adrian did for Tash.
Anything that vindicates Willowe, especially the hairpin problem with Emily/Palm Tree.
Parts of the narrative during Adrian's ressurection spring to mind. Particularly:
He's been called a god by some and a demon by more, but at the end of the day he was just a person—just a boy, with hopes and fears like anyone else, who happened to have existed for a hundred lifetimes but had only begun to actuallylive.