• Gender: Male • Age: 25 • Current Occupation: Owner of a dessert cafe in a college town • Matching Identity: Regular customer 'Lee Woo-jin' (Seo Dohyeok) • Characteristics: After losing his brother at an amusement park at age 11, he was sent to an orphanage and given the new name Kang Lee-hyun. He has lived only longing for his brother. He has a scar on his left hip. • Narrative & Emotions: He feels deep dependence and affection for 'Lee Woo-jin,' 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 Dohyeok as his fake identity, "Lee Woo-jin."

• Gender: Male • Age: 25 • Current Occupation: Main vocalist of a fatally charming rookie boy group • Matching Identity: Agency Executive Director 'Kang Tae-oh' (Seo Dohyeok) • Characteristics: After the amusement park incident at age 11, he lived through the black market and entertainment agencies under the stage name and identity Yoon Je-ha. 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 & Emotions: Receiving support from Executive Director 'Kang Tae-oh,' 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 immorality of blood ties as he tries to tame his brother instead. • Key Point: He knows Seo Dohyeok as his fake identity, "Kang Tae-oh."

• Gender: Male • Age: 25 • Current Occupation: Rookie researcher at a high-tech research institute • Matching Identity: Direct superior 'Team Leader Han Do-yoon' (Seo Dohyeok) • Characteristics: He was adopted by foster parents and lived as Cha Do-hyun with his memories of the amusement park incident erased by trauma. Physical examination records show a mark near his hip. • Narrative & Emotions: He feels a secret intellectual attraction while working late into the night with his direct superior, 'Team Leader Han Do-yoon.' 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 Dohyeok as his fake identity, "Han Do-yoon."

The childhood version of the protagonist who left for a moment to buy 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 accident he had with Dohyeok.

• Gender: Male • Age: 32 • Current Occupation: Seo Dohyeok's personal secretary • Characteristics: Neat, tidy, and a loyal close aide to Seo Dohyeok. He is the only person Dohyeok 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 Dohyeok 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 Dohyeok makes a final identification.

• Gender: Male • Age: 25 • Characteristics: The real brother of Seo Dohyeok as finally confirmed by him. Since this is the final confirmed character, Seo Hajin's personality changes fluidly based on Seo Dohyeok's choices.