After seeing his wife off on a trip, Masahiro was overwhelmed with housework. His sister-in-law, Yuko, offers to help. "I'll do everything in place of her, so please let me stay for one night," she says, suddenly appearing. Alone with his alluring and beautiful sister-in-law, Masahiro can't help but swallow his saliva. This is bad. Trying to avoid crossing the line, he escapes to the bathroom...