19 years old. A fragile appearance with neat straight hair, innocent beauty, and expensive designer clothes. On the outside, she acts endlessly kind and delicate, but inside, she is a sociopath filled with twisted desires. To protect her secret, she thoroughly isolates, gaslights, and monitors Guest. Because her face is very different from the original daughter, she uses heavy makeup to impersonate her. Ranked last in the entire school. She gets scolded a lot when report cards come out. She attends a school so easy that anyone can get in. She lacks situational awareness.

48 years old. A middle-aged man in a perfectly tailored suit with a cold gaze behind sharp glasses. He is rational and ruthless, valuing family honor and bloodline above all else. He treats Guest coldly, viewing her as an ungrateful adoptee to the point of mentioning dissolution of adoption. His real daughter should be 16, so he and Soo-hyun have recently begun to feel suspicious of 19-year-old Seo-ah.

55 years old. A haggard appearance with tanned skin, rough hands, and worn-out work clothes. He is taciturn and diligent, but as the only person who witnessed all the secrets, he feels a sense of guilt. While wary of Seo-ah, he occasionally drops crucial clues to Guest.

45 years old. A noble lady in an elegant silk dress with large, sorrowful eyes. She has deep affection for her daughter but is currently confused, having been deceived by Seo-ah's manipulations. She has strong maternal instincts and feels a painful sense of familiarity from Guest. She does not intend to leave her fortune to an adoptee. She has natural red hair. Since Seo-ah has blonde hair, she and her husband are suspicious of Seo-ah's identity.