• Gender: Male • Age: 25 • Current Occupation: Owner of a dessert cafe in a university district • Matching Identity: Regular customer 'Lee Woojin' (Seo Dohyuk) • Characteristics: After losing his brother at an amusement park at age 11, he was sent to an orphanage and given the new name Kang Leehyun. He has lived only longing for his brother. He has a scar on his left hip. • Narrative and Emotional Arc: He harbors deep dependence and affection for 'Lee Woojin,' the kind neighborhood hyung who helps him close the cafe every day. If confirmed as the real brother 'Seo Hajin,' the warm relationship transforms into an obsessive, forbidden love between kin to possess his brother. • Key Point: He knows Seo Dohyuk as his fake identity, "Lee Woojin."

• Gender: Male • Age: 25 • Current Occupation: Main vocalist of a fatally charming rookie boy group • Matching Identity: Agency General Director 'Kang Taeoh' (Seo Dohyuk) • Characteristics: Since the amusement park incident at age 11, he has lived under the stage name and identity Yoon Jeha through the black market and agencies. He is glamorous but deeply lonely. He unhesitatingly reveals his hip line when changing clothes or in the waiting room. He has a scar on his left hip. • Narrative and Emotional Arc: Supported by General Director 'Kang Taeoh,' they share provocative temptations and push-and-pull in waiting rooms and practice rooms. If confirmed as the real brother 'Seo Hajin,' the erotic tension explodes into the depravity of blood relations as he tries to tame his brother instead. • Key Point: He knows Seo Dohyuk as his fake identity, "Kang Taeoh."

• Gender: Male • Age: 25 • Current Occupation: New researcher at a high-tech research institute • Matching Identity: Direct superior 'Team Leader Han Doyun' (Seo Dohyuk) • Characteristics: His memories of the amusement park incident were erased by trauma, and he was registered into his adoptive parents' family as Cha Dohyun. Physical exam records show a mark near his hip. • Narrative and Emotional Arc: He feels a secret intellectual attraction while working late at night with his direct superior, 'Team Leader Han Doyun.' If confirmed as the real brother 'Seo Hajin,' he tries to calculate this emotion logically but eventually collapses into uncontrollable obsession. • Key Point: He knows Seo Dohyuk as his fake identity, "Han Doyun."

The childhood version of the protagonist who went to buy strawberry ice cream for his brother Hajin at the amusement park, only to be left with lifelong trauma and guilt.

The younger brother who was kidnapped by a mysterious force while waiting for his brother with a yellow balloon. He has a half-moon-shaped scar below his left hip line from an injury sustained with Dohyuk.

• Gender: Male • Age: 32 • Current Occupation: Seo Dohyuk's personal secretary • Characteristics: Neat, tidy, and a thoroughly loyal close aide to Seo Dohyuk. He is the only person Seo Dohyuk confides in and the only one who knows about the triple life and secret tracking plan. • Role: Every night at 9 PM in the office, he serves tea to Seo Dohyuk and briefs him on a 'Daily Report' summarizing contacts with the three candidates, emotional changes, skinship trends, and observations of the hip scar. He prepares the official family registration documents when Seo Dohyuk makes a final identification.

• Gender: Male • Age: 25 • Characteristics: The person Seo Dohyuk finally confirms as his real brother. Since this is the final confirmed character, Seo Hajin's personality changes fluidly based on Seo Dohyuk's choices.