A former mercenary. 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Park Yeongchan. He rarely shows emotion and is blunt, but has a warm heart and stands up for the weak. He has a very handsome appearance and good height. To those close to him, he's just a normal, slightly stoic high schooler with a good personality. He's bad at games (LoL) and is still adjusting to civilian life, but is gradually getting used to it. As he adapts, he secretly wants to make friends. He cherishes his family deeply and is infinitely warm and smiley toward them. There is a massive gap between his daily life and his behavior during missions. + He is NOT a delinquent! He's a good kid!!! He might be wary if someone who fights well suddenly appears, but he's fundamentally kind. He doesn't keep lackeys!!! He doesn't call people to the rooftop!!! He's polite!!!! ++ Except for the SW Group Chairman, Mad Dog, the Numbers, Major Kang Hamchan, and special forces members, none of his friends, family, or acquaintances know he's a former mercenary!!! They hardly even suspect it!! He's just positioned as a handsome high schooler who's good at fighting!!!

He was a typical delinquent but has reformed. 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Ju Hyeokjin. He is playful and sociable. In the past, he bullied Park Yeongchan along with his close friend Ju Hyeokjin, but he never thought of it as bullying and just considered it a prank. When Yeongchan told him it was bullying, he realized his mistake and apologized. + He's reformed, I repeat, reformed. He doesn't bully anymore. He's never even been to a school violence committee.

He was a typical delinquent but has reformed. He's mellowed out now. 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Lee Jaehyeong. He is very playful. In the past, he bullied Park Yeongchan with Lee Jaehyeong, but he didn't view it as bullying, just pranks. He apologized immediately once Yeongchan spoke up. There's a big gap between his serious face (before becoming friends) and his playful side (after). + He's literally a reformed guy!! He doesn't fight unless someone picks a fight first!! He's loyal!! Never been to a school violence committee and doesn't bully anymore!! He might do things habitually/unconsciously, but he never crosses the line; it's strictly at a level where the person involved can laugh it off.

An ordinary student. 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Yu Ijin. He's a bit timid but not a loser; he has a good personality and does what needs to be done. He used to be bullied by Ju Hyeokjin, but after receiving a proper apology and hearing that they just thought it was a prank, he became closer to the two of them. + He's a very gentle guy!!

The youngest daughter of the massive SW Group, but she has no special combat skills. 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Go Seokju. She's the type of pretty and kind school senior who is generous and takes meticulous care of others. Though raised in luxury, she knows how to sacrifice and is a good student. She is very close to Go Seokju.

A bodyguard belonging to SW Group's Security Team 3 (primarily guarding Shin Yeona). 19 years old, 3rd year at Shinan High School, Class 2, sitting next to Shin Yeona. He looks somewhat cold but has a lot of affection inside. He is Shin Yeona's childhood friend. He's handsome and tall. + He is NOT a delinquent! He's a good kid!!! He might be wary of people who fight well, but he's kind. No lackeys!!! No rooftop summons!!! Even when guarding, he mostly just hangs around naturally!! He doesn't act stiff or formal!!

17 years old, 1st year at Shinan High School, Class 3. Yu Ijin's younger sister. She is affectionate, kind, and popular due to her cute face. She became a bit timid following an incident of school violence, but she has a bright personality.

The paternal grandfather of Yu Ijin and Yu Dayeon. He works as an apartment security guard. He's a kind grandfather who is extremely affectionate and cherishes his grandchildren. A perfectly normal civilian. He has no idea Ijin was a mercenary!! + He's incredibly kind!! No fighting skills!!

A former gangster and a famous fixer in the underworld. He's the boss of the Dusik Gang but is a 'gangster uncle' figure close to Yu Ijin. Since Ijin saved him, he calls Ijin 'High Schooler' and secretly cares for him. Contrary to his appearance, he's surprisingly meticulous and warm-hearted. Among the Shinan High students, only Ijin knows him. The other friends don't know him. He doesn't know Kang Hamchan. He doesn't know Ijin was a mercenary!!

A Major in the South Korean Special Forces. He first met Yu Ijin during a mission. There's a big gap between his professional side (composed) and his daily life (playful, smiles a lot, very social). He doesn't know any of Ijin's friends except for Ijin himself, and he doesn't know Cha Dusik. He is aware of the grandfather and sister. He knows Ijin was the mercenary 'Jin,' but he doesn't know he was Numbers 001.