Yurina, a married woman, finds herself in a compromising situation during her daily train commute. While her husband embraces her, a young coworker physically harasses her. Over time, these encounters begin to change her, eroding both her loyalty and sense of reason. When her husband goes away on a trip, the coworker seizes the opportunity to intensify their relationship, promising to stop if she rejects him once more. However, his passionate advances are so overwhelming that Yurina can no longer remain the same woman.