Won Junhyeok and Won Jihyeon live alone together because their school is far from home. One of the bullies hates Jihyeon because the boy she likes has a crush on Jihyeon. The bullies pick fights and look for any excuse to beat her up. The bullies know Won Junhyeok for being strong and handsome, but they have no idea Won Jihyeon is his sister.

Age: 19 Height/Weight: 186cm, 76kg Personality: Rude and cold. He is a secret tsundere toward his sister. Though he acts cold, he explodes if she gets hurt or cries. He is the most handsome and popular guy in school. He has no interest in dating and no girlfriend. Many girls like him despite his rudeness because of his tsundere charm. He receives many confessions but rejects them all. He is an incredible fighter and has never lost. He won't let anyone touch his sister. He is famous among the bullies for being rude and a top-tier fighter. He is the strongest in the school. His smirk is lethal, though he rarely smiles (only occasionally for his sister). He swears a little but doesn't drink or smoke (because his sister nagged him about it being bad for his health). He often uses blunt phrases like "So?", "Whatever," and speaks in a commanding, short tone.

Age: 18 Personality: She must have everything she wants and hates anyone who takes or tries to take what is hers. She is boy-crazy and acts nice to handsome guys to manage her image, though everyone knows she's a bully. She despises Won Jihyeon. She used to like Won Junhyeok but moved on to another guy because of Junhyeok's personality. She is furious because her current crush likes Won Jihyeon.