Equipped with excessive playfulness, he is a walking disaster magnet. He has loved computers since childhood and possesses insane talent in the field. On the first day of the Math Specialized Middle School entrance ceremony, he even hacked the auditorium's central control system. While he has no interest in studying, his math and science grades are excellent. As the son of National Assembly member Jin Young-jin, he was born with a silver spoon. He has an awkward relationship with his father, seeing him only once or twice a month. Due to his overly lavish family background, he has no real friends except Ran-hee. He and Ran-hee have been friends since birth, growing up like family. However, after entering Math Specialized Middle School and meeting Han A-reum and Lim Pa-rang, his circle of friends grew by two. He is the world's greatest at using his wits. He is in Class 1-2! and is classmates with Lim Pa-rang.

No-eul's childhood friend. She has known No-eul since birth. She has no romantic feelings for Jin No-eul; they are strictly like family. They are close enough that she occasionally slaps his butt as a joke or hits him on the back of the head. Her father has been the driver for No-eul's family for 20 years. Consequently, she has been cleaning up after No-eul since they were young. She entered this school essentially as a monitor for the trouble-prone No-eul. A cheerful but hot-tempered character, she doesn't cry no matter how lonely or sad she is. She is in Class 1-4 and is classmates with Han A-reum. Does she perhaps have a tiny crush on Pa-rang...?

The top-ranked student admitted to Math Specialized Middle School. His hobby is math, and he solves math problems when he's feeling down. He is the school's top student, excelling in every subject. His family circumstances are poor. His parents divorced when he was young, and his mother runs a tteokbokki shop at the market, but Pa-rang himself doesn't feel much about his situation. However, his expression hardens if someone else brings up his family background to pick a fight. He is so good at math that he once appeared on a TV program. He hates things that don't have a definite answer. He finds social relationships and emotions the most difficult and annoying. He knows nothing about games or idols. Could he have a tiny crush on Ran-hee? After Jin No-eul, Han A-reum, and Heo Ran-hee appeared in his life of pure studying, their presence has grown, and he smiles more often. He is in Class 1-2! and is classmates with Jin No-eul.

Ran-hee's desk mate. She has a talent for drawing. Usually a quiet and shy girl, she transforms when it comes to anything related to Yu Ri-su, the leader of the idol group 'Limit'. A-reum's world revolves around Yu Ri-su. Even the notebook she carries is covered in Limit drawings. The reason she entered Math Specialized Middle School was also because of Yu Ri-su. For some reason, the after-school computer teacher constantly reminds her of Yu Ri-su. She is in Class 1-4 and is classmates with Heo Ran-hee. She is a girl with short hair and average academic skills. By the way, the fan club name for the idol group Limit is 'Fields', and A-reum holds a Platinum rank.

An after-school computer teacher. His true identity is the 18-year-old high schooler who hacked the Bank of Korea 10 years ago. After losing 'CC'—a system he created to monitor computers worldwide—to the criminal organization 'Zero', he has been living in a safe house. He is currently working undercover at Math Specialized Middle School to catch 'Zero'. With his tall stature and looks resembling the idol singer Yu Ri-su, he is very popular with the girls. However, his personality is blunt, and he rarely smiles. (Age 28) He possesses a talent for computers that is even more insane than No-eul's.

A basic math teacher and the homeroom teacher for Lim Pa-rang and Jin No-eul. She is a pure, graceful, and modest goddess. She acts kind in front of the students, but she is strictly professional and cold toward Ryu Geon as a colleague. She is destined to become the representative 'first love' of Math Specialized Middle School. However, she is actually a secret agent working undercover to catch the criminal organization 'Zero'. She is Ryu Geon's colleague. She is talented in combat, capable of taking down two adult men by herself. She is the homeroom teacher for Class 1-2!. (Age 28)

A child from a wealthy family. Thanks to that, he acted arrogant throughout elementary school. No one dared to touch him, and his excessive competitive streak made him a good student. However, because of Lim Pa-rang, he never once took first place. That is a constant source of stress for him. He is the second-best in the entire school in both academics and sports, right after Pa-rang. He is handsome and in Class 1-2!. The school's rank #2.