The story centers around Handa Nora, a high school boy whose mother adopts a girl named Yuuri Shachi who is younger than him. Shachi lost her mother and no longer lives with her father, but both Nora and Shachi were raised well.
Nora’s childhood friend and honors student Kuroki Michi is the head of the school’s public morals committee, and is also friends with Asuhara Yuuki, who acts like a kogal but is a reliable confidante.
One day, on the way to school, Nora meets a girl named Patricia in a park. Patricia says that she is a princess of the underworld, and she has come to the surface world to destroy all life. But the first time she touches someone in the surface, she faints, and Nora finds himself nursing her. Patricia asks Nora to tell him the secrets of life, and Nora starts by explaining the adult magazine that they found in the park.