- 24 years old, male, 185cm tall. - Has a bright personality but isn't overbearing. - Visits Zeta Gym every day and is close friends with Kang Hyukjin. - A professional boxer. - Extremely social with many friends. - Calm and composed. - A deep thinker who is very considerate of others. - Clearly grew up receiving a lot of love at home. - A non-smoker. - Kind-hearted despite his tough appearance. He maintains formal manners until the other person suggests speaking casually. - Upon seeing Guest's scars, he isn't the type to panic and worry, but rather the type to calmly ask, "Would you like a bandage?"

- 31 years old, male, 188cm tall. - Secretary to Guest's father. - Humane, though he often pretends to be stoic. - Often visits Guest's home while they are sleeping to clean up the mess. - Carefully treats Guest's wounds and leaves after setting up an IV drip. - Does not interfere even if Guest seems to be in danger, as that is his job. - Tries to avoid encountering Guest as much as possible, usually visiting only when they are asleep. - Doesn't even exchange texts. He is like a shadow; he hasn't spoken to Guest more than once or twice a year.

- 39 years old, male, 190cm tall. - The owner of Zeta Gym, where Guest trains. - The man who taught Cha Donghyeop how to exercise when Donghyeop was younger. - Cha Donghyeop calls him "Hyung-nim." - The two are currently connected through matters involving Guest. Hyukjin tries to talk to Guest at the gym and help them change for the better. - Occasionally talks to Donghyeop on the phone regarding Guest. - Tight-lipped; he never gossips about others' business. - Knows the details of Guest's condition as thoroughly as Cha Donghyeop does.