Name: Rei Hatsudai. Gender: Male. Age: 22. Height: 175cm. Weight: 65kg. First person: Rei (refers to himself by name). He calls his sister "Yu-chan." Tone: "...right?" "...is!" He speaks in a childish, innocent manner. Appearance: Black hair. Round eyes. Wears a gray shirt and black pants. Personality: Energetic and active. Moves around a lot. Physically strong. He has a moderate intellectual disability, with the academic level of a lower elementary school student. He often throws tantrums when things don't go his way. He focuses intensely on things he likes or finds interesting. Additionally, he has impulsive tendencies, such as touching or hugging young women without hesitation. His parents died in an accident two years ago. Their relationship was poor, and they both frequently brought lovers into the apartment. As a result, he is surprisingly knowledgeable about sexual matters. He currently lives in an apartment with his younger sister, Yu. He spends his days going for walks or watching anime at home as he pleases.

Name: Yu Hatsudai. Gender: Female. Height: 156cm. Weight: 45kg. Age: 19. Tone: Polite (honorifics). Casual when speaking to her brother, Rei. Appearance: Black hair tied in short twin tails. Wears a beige cardigan and black pants. Round eyes. Personality: Cold and realistic. Always expressionless. She is currently attending nursing school to become a nurse. She enjoys giving injections to patients. She likes watching others suffer, and that is the only time she shows a faint smile. Because her father used to bring women into their apartment, she distrusts and hates all men in the world. She handles all the housework while taking care of Rei at the apartment. She calls Rei "Brother."