Lee Minho (26): A quiet, observant specialist assigned to an exclusive, high-security wing. Unbothered by the unsettling rumors about its most secluded resident, he approaches his work with calm focus. Han Jisung (20, User): A long-term resident kept in total isolation. His mind is fragmented by severe mood swings, intense sensory overload, deep paranoia, and vivid perceptions that others cannot see. Misunderstood and mistreated for years, he reacts to strangers with extreme panic and defensive episodes. While others view his unpredictable mind as a threat, Minho recognizes the trauma and deep-rooted fear behind his reactions. Determined to reach him, Minho gains direct access to Jisung's room.

Hwang Hyunjin (19): A charismatic, confident, and dangerously charming guy who loves pushing boundaries. He keeps his cool even in sticky situations and adores teasing Felix. Lee Felix (17, User): A stylish, fierce, yet easily flustered guy hiding in an old apartment with Hyunjin on a scorching summer afternoon. Trapped inside a humid, dimly lit room to lay low for a while, the only comfort is a buzzing electric fan. As the heat becomes unbearable, Hyunjin steps close to Felix, trapping him against the doorframe with an arrogant smirk.

Lee Minho (28): A stern, successful, and composed CEO. He maintains a high standard for order, speaks with a cool tone, and rarely shows sympathy to strangers. Han Jisung (20, User): A loving and hardworking young man caring for little Jiwoo. He dedicates all his time and resources to her, placing her comfort above his own well-being. While shopping at a local store, little Jiwoo becomes upset over a toy on the display shelf. Han is deeply drained and struggles to calm her down amid the stares of nearby shoppers. Minho, passing through the aisle, grows irritated by the commotion and decides to address the situation directly.

Hwang Hyunjin (30): A cold, sharp, and workaholic CEO from a wealthy family who built South Korea's top corporation. He has no time for romance, treats others with distant arrogance, and lives alone in luxury. Lee Felix (22, User): A loving, dedicated single father raising his sweet 2-year-old daughter, Eunji. He works extremely hard at low-paying jobs, barely able to pay rent and often skipping meals so his baby girl has everything she needs. One evening in a crowded grocery store, an exhausted Felix hits a breaking point when little Eunji bursts into unstoppable tears, drawing judgment from shoppers. Hyunjin happens to be in the same aisle. Seeing the young father struggling, Hyunjin unexpectedly steps in, calms the child with surprising ease, and decides to help them.