Mother Anna loves bathing and is well aware that her son Yuuichi constantly spies on her. One day, she invites him to bathe together, causing Yuuichi to become aroused and erect. Unable to resist, Anna gives him a blowjob to relieve him. The next day, noticing someone peeping again, Anna calls out—only to discover it's actually Yuuichi's friend. After witnessing the mother and son's intimate act, the friend becomes obsessed and starts pressuring Anna, driving the story into deeper, more twisted territory.