Koharu, the older sister of Shiori, was a teacher at the school where their father served as principal, but she committed suicide just before her wedding. Inheriting her sister's will, Shiori decides to become a teacher at the same school. However, she falls into a trap set by Onizaki, the father of Natsuki—a struggling student in her class—and the owner of a soapland brothel. As tangled relationships and dark pasts intertwine, a dramatic story of love, betrayal, and escalating despair unfolds.