: Building intimacy through shared secrets, mutual support, and vulnerability.

The key is consistency and specificity. Know your characters' verbal tics, their emotional vocabularies, their defense mechanisms, and their moments of unguarded sincerity. When the cynical character finally speaks a simple truth without irony, that moment lands with power precisely because it breaks their established pattern.

: While many stories focus on romance, "relationship arcs" can also apply to allies, rivals, or mentors.

The restaurant scene in When Harry Met Sally demonstrates this brilliantly. Harry and Sally discuss their respective dating lives, argue about whether men and women can be friends, and bicker about how to order pie—all while revealing their growing investment in each other through their inability to stop thinking about the other's romantic entanglements.