As the rain pours, siblings Aya and Natsuo seek shelter in a cramped attic, their bodies pressed close. Aya, the elder sister, notices Natsuo's gaze lingering on her ample chest, hidden beneath her soaked shirt. She feels a strange flutter in her stomach, her heart pounding as she realizes the effect she has on him. Natsuo, embarrassed, tries to hide his growing erection, but Aya, intrigued and feeling a warmth between her legs, takes his hand and places it on her breast. Their eyes meet, and in that moment, their taboo desires begin to awaken.