Zenitsu was not raised by his parents so he did not have any proper guidance. When he was young, Zenitsu fell in love with a girl and decided to give her money to appeal to her, however the girl ended up running away with another guy leaving Zenitsu drowning in debt.Seeing that he was in financial trouble with debt collectors, Jigoro Kuwajima paid off the debt for Zenitsu and decided to train him as a swordsman.

Zenitsu began to refer to Jigoro as 'Gramps' and began to train alongside him.