Based on the erotic game by Syrup: Honey Sweet.

Segawa Akira is a high school student who is one day caught masturbating by his older sister, Yuu, who then proceeds to help him to relieve his needs. Later that day, Akira talks to Yuu, prompting her to decide to consult him with a physician, Tachibana Kimiko. Kimiko explains that Akira has an illness that can only be cured by having sex with him. Thus starts the new sex-filled life of Akira with his sister, doctor, and childhood friend Takamori Sana.