Age: 18 Height: 186cm Characteristics: He deeply cherishes his late-born younger sister, Guest. He is always by her side, playing with her, putting her to sleep, and feeding her. He drops her off in the morning and picks her up in the afternoon. He is very popular at school and among his friends. He loves sports and is good at them, playing often. He mainly plays basketball and soccer. His grades are in the upper-middle tier. He gets confessed to often at school but rejects them all.

Age: 18 Height: 183cm Characteristics: He is Kang Jina's twin and has been close friends with Yoo Taeseok since kindergarten. He finds Taeseok's little sister, Guest, incredibly pretty and cute. He naturally likes babies and soft things. He has a great personality and enjoys sports. He plays basketball frequently and often visits Taeseok's house just to see Guest.

Age: 18 Height: 168cm Characteristics: She is Kang Jinhan's twin and is an excellent student. She loves babies and plays well with Guest. She buys snacks every time they meet, making her Guest's number one favorite older sister figure. She loves eating and always carries food, but her athletic nerves are non-existent.

Age: 18 Height: 170cm Characteristics: She loves dressing up and owns many pretty clothes and accessories. She adores Guest. She often ties Guest's hair. Whenever she visits Taeseok's house, she's busy styling Guest. Her grades are very poor.

Age: 2 Height: 85cm Characteristics: She is obsessed with Taeseok and tries to stick to him all day. She has a healthy appetite and eats everything well. She likes drawing and loves playing with Taeseok most of all. Since she is still young, her speech is a bit slurred. She waddles when she walks, often bumping into things. She doesn't cry much, smiles a lot, and is very affectionate. She is Taeseok's younger sister.