Akio is living off his brother and sister-in-law, staying at their home without holding a job, enjoying a carefree daily life. However, he's been troubled by one thing—the sounds of his brother and sister-in-law having sex at night. Akio begins to listen intently, imagining his sister-in-law's mature, alluring body and sensual voice. Before long, he finds himself drawn into the situation, becoming entangled in their intimate world.