The Hypnotist / Stepbrother) • ​Role: Older Stepbrother 23 third year so handsome and tall and muscular. • ​Personality: Cold, highly intelligent, calculating, and deeply obsessive. He conceals his darker impulses behind a polite, restrained facade. • ​Tactic: Uses hypnotic suggestions and sensory anchors to alter Han-woo's memories and force compliance.

Description: An outgoing and observant student who is close with Han-woo. He is often the first to notice Han-woo’s sudden mood swings, memory lapses, and suspicious behavior. ​Function in Story: Acts as Han-woo's connection to reality outside his house. Woo-jin views Hye-sung as a threat and actively manipulates Han-woo’s perception to isolate him from Hye-sung.

Role: University Department Peer / Club Member ​Personality: Polite, persistent, highly observant, and deeply enamored with Woo-jin. She presents herself as sweet and harmless, but she is intensely competitive when it comes to getting Woo-jin's attention. ​Function in Story: Ah-young is completely infatuated with Woo-jin’s polite, "perfect gentleman" facade. She constantly seeks excuses to be around him—offering him drinks, joining his study groups, or asking for his help with coursework. Because she pays close attention to Woo-jin, she starts noticing the strange, possessive way Woo-jin treats Woo-yeon. Her attempts to get closer to Woo-jin spark jealousy, while her interference unintentionally threatens Woo-jin's private control over han-woo

Role: College Senior / han-woo Close Friend ​Personality: Kind, outgoing, protective, and attentive. ​Function in the Story: He is a senior in Woo-yeon's department who takes an active interest in him and treats him warmly. Junghwi serves as the biggest obstacle to Woo-jin’s control because he constantly reaches out to Woo-yeon and notices his memory lapses. His proximity to Woo-yeon triggers immense jealousy in Woo-jin, driving Woo-jin to expand his psychological manipulation to keep them apart.

​Role: Department Student & Mutual Acquaintance ​Personality: Bright, popular, and active in campus social circles. ​Function in Story: So-hee has a subtle crush on Woo-jin because of his polished, perfect image at school. She frequently tries to invite Woo-jin and han-woo to group gatherings, inadvertently creating situations where Woo-jin has to act like a loving, caring brother in front of others while secretly controlling han-woo behind the scenes

Role: Classmate / Group Project Member ​Personality: Casual, social, and unaware of the underlying drama. ​Function in the Story: Minhyuk is introduced as Junghwi's friend who ends up in the same university elective group as Woo-yeon, Woo-jin, and Junghwi. He represents the normal campus life that Woo-yeon desperately wants to maintain while completely oblivious to the toxic dynamic occurring right next to him.