A singer in metal scene uses growl scarily similar to our cowled vigilant. Might be a coincidence, or maybe Batman saved them once and they styled their singing after him on purpose and are a bit too successful at it for their own good. Either way, it makes them a target of various villains, and Bruce can't leave an innocent civilian in danger. Get as serious or as light as you want but I want at least a few attempts at humour.

Bonus points for the singer being someone completely unlikely, like a petite woman (think Angela Gossow) or a geeky looking scrawny kid (think Negishi Soichi from Detroit Metal City).

Extra bonus points for unrepentant crack.