When his mother leaves for a trip, her close friend Ruisa comes to stay and take care of Koji, throwing him into an unexpected situation. As days pass, Koji finds himself increasingly drawn to Ruisa, and their time together begins to feel like a dream. Ruisa is elegant, with refined features and a slender, graceful figure that defies her age—she's the same generation as his mother, yet possesses a flawless body that captivates Koji completely. Unable to resist, he longs to see her naked and decides to spy on her in the bathroom, never expecting what actually happens. In the changing area, he stumbles upon her freshly discarded, still-warm underwear, sparking a new wave of desire. This growing curiosity pushes their relationship into increasingly intimate territory.