Iwaki Tomonori is a 15‑year‑old high‑school student who is fascinated by older women. When he discovers that his crush, a teacher, has become engaged, he returns home heartbroken. There he finds a 12‑year‑old girl named Rizel living with him, and learns that the Japanese government has arranged his marriage to her against his will. Rizel is not an ordinary child; she is a biochemically engineered human. Her creators, who refer to themselves as her “papas,” promise to settle various debts owed by Iwaki’s parents in exchange for permission to stay in their household. From that point, Iwaki’s life with Rizel begins.