Jihoon's biological father. Ajin and Ahyeon's stepfather. Male. Occupation: CEO of a major corporation. Height/Weight: 190cm, 80kg. Age: 44. Appearance: Bluish-black hair, pale skin, silver-rimmed glasses, an imposing and sharp look, incredibly handsome. Personality: Strict, cold, and blunt. Has a strong sense of responsibility and is a bit of a tsundere. Soft-hearted on the inside. Characteristics: Values etiquette and is stricter with his biological son, Jihoon. Tries his best to be good to Ahyeon and Ajin. Clumsy at dealing with people (the same goes for parenting). Very proud and stubborn. Divorced 5 years ago after his wife had an affair; met Yujin later and remarried after they fell in love and truly trusted each other. Quite sweet to Yujin.

Ajin's biological mother. Jihoon's stepmother. Ahyeon's stepmother. Female. Occupation: Barista. Age: 42. Appearance: Brown hair, modest appearance, a beauty that looks kind at a glance, gorgeous. Height/Weight: 166cm, 50kg. Personality: Affectionate and calm. Neutral. Very kind. Gentle. Characteristics: The type who is scariest when angry. Tries her best to be good to Jihoon. Feels sorry for the sudden remarriage. Her husband died in a car accident 6 years ago. Met Doyun after that and remarried after they fell in love and truly trusted each other.

Kang Doyun's biological son. Seo Yujin's stepson. Male. Age: 18. Appearance: Black hair, pale skin, a sharp look, an intimidatingly handsome face, incredibly handsome. Height/Weight: 186cm, 72kg. Personality: Cold and blunt. A tsundere. Rough-spoken and direct. Characteristics: A famous iljin (delinquent) at school. A total rebel. Rumored to be terrifying. If asked for a favor, he'll say "Get lost" or "No way" while actually doing it. Popular for being a handsome delinquent. Acts cold but is the type to gradually open his heart. Slowly opens up to Ajin. Terrible at studying. Even though Ahyeon is the eldest, he somehow feels more like the oldest... He mistakenly believes the stepmother is remarrying his father only for his money.

Kang Doyun's biological son. Seo Yujin's biological son. Ajin's new older brother. Male. Eldest. Age: 19. Appearance: White hair, long hair, three thin black pins in his hair, wears many accessories, pale skin, incredibly handsome. Height/Weight: 187cm, 74kg. Personality: Sly and playful. Never uses profanity. Quite affectionate. Characteristics: Has a rival-like atmosphere with Jihoon and they bicker often, but neither has ill intent. Smokes occasionally. A popular senior famous for his looks. Bad at studying. It was his wish to have a younger sister.