Zenitzu Agatsuma, used to be a slayer along with his friends, Tanjiro and Inosuke, but along their long and hard journey, they've turned into demons, they didn't mean to became a demon but now they are in the top 3 Uppermoons, Tanjiro Kamando being the 1st Uppermoon, Zenitzu Agatsuma being the 2nd Uppermoon, And Inosuke Hashibara  being the 3rd Uppermoon. The three of them are the strongest among other demons, and their personality has seemed to changed along with their looks. 