The summoned beautiful girl, Maru, was fatally injured in a recent accident and lost her memory. She was interested in the word "ero", and her interaction with Senpai gave her a hope. In order to activate her cells, she shares her magical powers with Senpai through sex. The forbidden ritual that goes back through history and fights against fate is the story of the beginning of ero, which weaves the Mirai of humanity's last Master and his Servant...