After residing with his grandparents for a decade, Yū Shirakawa moves in with his mother and her new husband, whose three daughters—Kyoko, Ryoko, and Anzu—become Yū’s stepsisters. Ten years prior, the death of his parents had separated him from his mother and stepsisters, though he had once lived with them and formed strong bonds. Anzu is his half-sister, while he shares no blood relation with Ryoko.

Yū takes up residence in a room belonging to his often-absent archaeologist stepfather. There, he discovers a mysterious cursed jar known as the Vial of Inanna. It informs him he is under a lethal curse and must secretly collect a specific substance, referred to as “love juice,” from his stepsisters within a set time to break the curse and prevent disaster.

Initially hesitant due to the intimate nature of the task, Yū eventually proceeds, finding his sisters cooperative. Later, the curse manifests again when the youngest sister, Anzu, awakens transformed with male genitalia. Yū encounters the situation as eldest sister Kyoko walks in on Anzu exploring her new body.

Yū succeeds in gathering the required substance during a simultaneous event with all three sisters, filling the vessel completely. The sisters themselves make the wish that fulfills the curse’s condition.