Most of the Bruno/Reader stuff I've come across leans into the whole 'bodyguard of hearts' vibe, which honestly makes a ton of sense given his character. You get a lot of fics where the reader is someone under Passione's protection, or maybe a civilian who accidentally witnesses something they shouldn't. Bruno's sense of duty and protectiveness gets cranked up to eleven, but with this underlying tenderness he only shows when nobody's looking. It's not just action-packed rescues, either. I've seen really quiet moments where he's just mending a coat for the reader after a mission, or teaching them how to make that perfect espresso he's always drinking. The appeal is in that contrast—the ruthless capo who's also incredibly gentle with one specific person.
Lately there's been a wave of 'missing moments' fics set during the Venice arc, imagining what could have happened if the reader was there on the boat with him. Those tend to be heavier, angsty, soaked in that pre-dawn light and the smell of the sea. They explore his willingness to sacrifice everything, and the reader trying to cope with that self-destructive nobility. It's painful, but in a way that feels true to 'JoJo's Bizarre Adventure'—melodramatic and raw and oddly beautiful.
You also can't ignore the 'Sticky Fingers' fics. People get creative with his zipper ability in surprisingly intimate ways. Unzipping a wall to sneak into the reader's room, or using it to carefully remove a piece of clothing stuck to a wound. It becomes an extension of his care, another language for his affection. It sounds weird out of context, but in the fandom, it just works.