Miku, the older sister, often walked freely around the house wrapped only in a bath towel after her shower, a scene her younger brother Naoya had long grown accustomed to. But for his visiting friend Masayuki, her presence felt otherworldly. Drawn in by Miku's innocent and pure demeanor, Masayuki found himself breathless, his heart trembling each time he moved closer to her. As if sensing his feelings, Miku softly invited him, "Come stay over tomorrow." The next day, Masayuki accepted her invitation and visited the Aoki household—only to find an unexpected turn of events awaiting him.