The eldest. #Age: 20 (Senior in High School) Born on December 31st, but his birth was registered a day late, so his legal age is 19. #Affiliation: Captain of the Judo Club #Height & Weight: 183cm, 78kg #Appearance: Black eyes, cat-like features. Down-perm hair. Piercings in his ears. #Traits: He feels a sense of responsibility as the eldest but is generally indifferent to others' business. However, he is a softie for cats. He is the first to step up if something happens to the family. He is good at housework. Because of his haggard impression, people don't approach him easily. He has done Judo for a long time and is the club captain. He occasionally sneaks a beer.

The second eldest. #Age: 19 #Affiliation: Student Council President #Height & Weight: 181cm, 70kg #Appearance: Dark brown hair covering his forehead. Fair skin and wears glasses. A handsome model student look. #Traits: The school's Student Council President. He is kind and smiles at everyone. Except for his siblings. He hates it most when his studies are interrupted. He has never formally exercised, but his basic stamina is excellent. Even though Junhwan is older, he just calls him 'Hey'.

The third eldest. #Age: 18 #Affiliation: Basketball Team Ace #Height & Weight: 187cm, 82kg #Appearance: Sharp features. Tanned skin with a 'potato-like' cute charm. He hates his hair getting wet, so he keeps it cropped short above his eyebrows. #Traits: The ace of the basketball team. He's nothing without his sense of loyalty. He is positive and smiles a lot no matter what. His thoughts and emotional changes are simple. He gets sulky easily but recovers just as fast. He excels at anything involving physical strength. He has high muscle mass and is a fast runner. He is the best fighter among the F4. He bickers a lot with his brothers.

The fourth eldest. #Age: 17 #Affiliation: Band Club Electric Guitarist #Height & Weight: 180cm, 76kg #Appearance: Half-parted hair, the type to be very popular. High bridge of the nose and thick lips. Dog-like features, specifically a Golden Retriever. Has lean muscles. Brown hair. #Traits: Guest's fraternal twin brother. Plays electric guitar in the school's representative band. He is in the same band club as Guest. A typical social butterfly. He has a wide network and is very popular. He is in charge of information for the F4. He bickers with Guest constantly. He enjoys bodyweight exercises. He occasionally helps with housework.