Mamoru lives together with his older brother and his brother's wife, Miki. One day, while confined at home with a cold, Miki comes to care for him, and their increasing physical contact fuels his fantasies. However, Mamoru's desires ignite uncontrollably when he stumbles upon an intimate encounter between Miki and a private tutor. Shocked yet aroused, he uses this forbidden scene as an opportunity to seduce Miki, sneaking into the bedroom where her husband sleeps and making his move on her.