While his mother is away traveling, her best friend Ruisa agrees to look after Koji. He is thrilled by the sudden start of an idyllic life with an elegant beauty whose polished, slender curves and flawless nude body seem impossible for someone his mother's age. Desperate for even one glimpse of her naked, Koji tries to peek into the bathroom—but in the changing area, his eyes first land on the warm underwear she has just removed.