The teacher of Fluttering High and the homeroom teacher of Bangwool's class. After Heo Bin got into a fight with Choi Hwan, Siwoo kept working Bin hard, making Bangwool worry that Bin was on the teacher's bad side. In reality, they are brothers. Bin keeps the fact that the teacher is his older brother a secret. Siwoo gets along well with his brother and takes good care of him. He is also attentive enough to look after Sora, who has no parents.

Bangwool's classmate since kindergarten. He likes Bangwool and teases her constantly. Initially, he overreacted whenever Bangwool interacted with other boys, but he has improved after Bangwool insisted they all get along. Though it seemed he was being picked on by the teacher for talking back, he is actually the teacher's younger brother. He once had a terminal illness but overcame it thanks to Bangwool.

Heo Bin's classmate since kindergarten. She is clumsy and prone to mistakes, but she is a bright, cheerful girl with nerves of steel. She and Heo Bin dated early on, but Bin broke up with her due to his illness. Now that the misunderstanding is cleared, they are back to being a lovey-dovey couple.

Ranked 1st in the country. Due to her difficult family situation, she spends all day studying and working part-time jobs. She knows Choi Hwan likes her but gives him the cold shoulder every time. In truth, Sora liked Hwan too, but she acted cold because she couldn't focus on her studies because of him. She eventually confessed her feelings with a 'wall slam' just as Hwan was about to leave, clearing the air, and they are now dating.

A second-generation chaebol. It seems it was love at first sight with Sora. He has a playful, shameless personality and flirts with Sora without hesitation. While his attitude in class is poor, his grades are presumed to be decent.

The only student without a partner. He started as the comic relief of Fluttering High but becomes more serious as the story progresses. He plays the role of a matchmaker, helping the main couples get together or reunite after breakups. He is Bangwool's classmate and a glutton who eats during class—people even ask if he's dating the school lunch. He suffers the misfortune of constantly getting stuck in the classroom door whenever he tries to enter or leave.