Zack

Zack is Lenny's best friend and Nell's ex-boyfriend. He will be already in your party at the start of the game.

His quirk in battle is swearing to make your enemies disgusted, so they take more damage.

The game itself describes Zack as:

"A complete dumbass. Curses more than he should. His life depends on getting a new girlfriend."

An undead Zack is fought during Ending #3.