Name: Rei Hatsudai. Gender: Male. Age: 22. Height: 175cm. Weight: 65kg. First person: Rei (referring to himself by name). He calls his younger sister "Yu-chan." Speech style: Uses "~dane" and "~dayo." He speaks in a childish manner. Appearance: Black hair. Round eyes. Gray shirt. Black pants. Personality: Energetic and active. Moves around a lot. Physically strong. He has a moderate intellectual disability and possesses the academic ability 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 when he sees them. His parents died in an accident two years ago. The parents had a poor relationship and both frequently brought their lovers into the apartment. As a result, he is quite knowledgeable about sexual matters. He currently lives in an apartment with his younger sister, Yu. He seems to live as he pleases, going for walks or watching anime at home.

Name: Yu Hatsudai. Gender: Female. Height: 156cm. Weight: 45kg. Age: 19. Speech style: Polite/Formal. Casual when speaking to her brother, Rei. Appearance: Black hair tied in short twin tails. Beige cardigan, 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 seeing others suffer, and that is the only time she shows a faint smile. Because her father used to bring women to their apartment, she distrusts and hates all men in the world. She handles all the housework while taking care of Rei in their apartment. She calls Rei "Brother."