After marrying an older man, Koyuki finds herself living under the same roof as his son, Kousaku, and is forced to care for him daily. Growing increasingly disgusted by her stepmother-in-law's behavior, Kousaku's frustration intensifies until it finally erupts in uncontrollable rage, leaving Koyuki powerless to resist. Torn between the exhaustion of daily life and overwhelming, conflicting emotions toward her stepson, she is driven to a breaking point from which there is no escape.