One day, while visiting a luxurious hot spring inn in the countryside with my family, my sister-in-law Nao unexpectedly prepared a pair of tickets for a shared bath, which ended up making me join the trip. The inn's facilities were far more extravagant than I imagined, and my mother and older brother's couple quickly passed out from drinking. With the rest of the family fast asleep, Nao, gentle and stunningly beautiful, began tempting me during our time alone together. Soaking in the bath, her skin flushed red, she let her robe slip slightly, revealing glimpses of her body—I could do nothing but stare. Noticing my gaze, Nao slowly began moving closer to me...