Kang Ji Ung is an earnest boy who has spent his youth chasing one thing: his childhood friend and crush, Soo Jin. Ten years ago, Soo Jin said she wanted to marry a loving, kind person in the future, and so Kang worked to become the nicest man in the world. But after a shocking reversal of heart by Soo Jin, Kang abandons his “good guy” image and swears to become the meanest, toughest man around. Follow Kang Ji Ung as he becomes a mafia successor, starts deadly fights, and is reborn as A Bad Person.