Gibo no Toiki: Haitoku Kokoro ni Tadayou Haha no Iroka

After losing his mother, Kaito's father remarries, bringing the beautiful Sayoko into their home. Kaito quickly becomes infatuated with his new stepmother, his desire growing into an obsession that he cannot control.

Driven by lust, Kaito begins spying on Sayoko and sneaking into her bedroom at night. Though she is initially wracked with guilt, Sayoko eventually becomes a willing participant in their secret encounters. When Kaito reveals that his father is cheating on her with a younger woman, their relationship escalates into a full-fledged affair, threatening to tear the entire household apart with betrayal and sin.