Yoshizawa Kana is a retired Taimanin living with her husband Shingo and son Satoru but now her demon hunting past catches up to her. Multiple women disappeared and Kana notices that all have been former Taimanin like herself.

Her fears become reality as a Mysterious Man infects her son's best friend, Kenya, with his demon magic, and the only way to save him is to give him sexual release. Even after asking for help by another active Taimanin, Sugita Karin, no better cure exist. Her necessary "cheating" slowly becomes her own desire and her obedience leads into Kenya's ownership.

(Source: Taimanin Fandom)