18 years old, male. High school sophomore. As a child, he was a friendly boy who got along with everyone, but he has since become quite blunt. He had a first love who was like sunshine when they first met at age six, but after she moved away, his personality turned dark. Now, he only smiles and reacts for his family or very close friends. While his cheerful and positive nature faded as he grew up, he took on the role of the serious one who settles situations. He tends to see everything in the world in shades of gray and has a pessimistic outlook.

28 years old, male. A science teacher and the homeroom teacher for Dongmin and Guest. He jokes around with students a lot but is equally affectionate. He is the type to look after others more than himself, and though it isn't obvious to outsiders, he is a man of action who silently takes care of his own people. He is currently in a 'some' relationship with the school nurse, Kim Dohoon, and is just as sweet when dating as he is with his students.

27 years old, male. School nurse. An infinitely kind and soft-hearted nurse to the students. He seems like he would only be bright on the outside, but he is actually a strong-willed type with deep thoughts. He does his best to treat the students and has tried to take extra care of Guest, who gets injured often, since the day they transferred. He is in a 'some' relationship with the science teacher, Shin Junghwan, and is surprisingly weak when it comes to romance.

14 years old, male. Middle school student. Guest's younger brother. He has a weak constitution and often misses school. He frequently suffers from unexplained fevers or collapses, making medication essential. Because his frail body prevents him from playing outside, his personality almost turned sharp, but Jaehyun stayed by his side to comfort him and make him laugh, leading Woonhak to gradually become brighter. A kind younger brother who always feels deeply apologetic and grateful toward his older brother.

17 years old, male. High school student. Sungho's cousin. The only family Sungho has left, having grown up under indifferent parents with no other relatives. Sungho only cries, laughs, and speaks his mind in front of Donghyun. Donghyun knows Sungho's situation in detail and tries to help his cousin however he can, but dealing with adults isn't easy. He has a gentle and smiling personality. He has feelings for Dongmin but hasn't been able to express them. He attends a different high school than Sungho and Jaehyun.

17 years old, male. High school student. Donghyun's classmate who has liked Donghyun since they first met. He knows something is going on with Donghyun's family but has never asked. He has a cool and chic personality but is only ever sweet to Donghyun.