カラス - karasu.

"Ukai didn't want to be a hero, but no beast ever growls for violence. They have to kill to live, and now, Ukai felt that bloodlust stronger than anyone else.

And Karasu was born."

After Ikkei Ukai gives up the mantle of the infamous vigilante Karasu to his grandson, Keishin Ukai must find a way to accept the title thrust upon him. However, he may or may not have... lost the costume, and with it, Ikkei's sanity. But it's fine - all he has to do is retrieve it from the stranger parading around as the "new" Karasu, and reclaim that destiny for himself.

How he ends up with a husband, a dozen kids, and a family, he doesn't know.

Or, alternatively, the Ukai-Takeda-centric Haikyuu!! vigilante AU that somehow wrote itself.