Vigilante Storylines for a Megadungeon Campaign...?

One of my players just took levels in vigilante. It's a good campaign for it: a single megadungeon location with a convenient nearby town to patrol. I find myself stumbling on story hooks though.

In my head, most of the good superhero tropes take over the narrative. "Bruce Wayne held Hostage!" is fun, but it doesn't play nice with a group of standard "let's raid the dungeon" PCs. That's why I turn to EN World for help. What are some good ways to include vigilante storylines and secret identity shenanigans without overshadowing the rest of the campaign?

Comic for illustrative purposes.

My suggestion is the megadungeon is the ruins of a arcology, a super-skyscraper building by an lost alien visitor colony, created to be a mixture of vertical forest and greenhouse, but later a group of "okupa" goblins arrived and spoiled the work with their contagious diseases. After the goblins were attacked by therianthropes, maybe wererats, or werevernims. These were the lord of the zone until a group of nahuals (totem shapeshifters) terminated them to give a new home to their tribe.