Out of teenage Kokoro, the younger sister and her friend end up watching some adult videos and books in their older brother's room. It's the first time they've seen such shocking images. Lust enters the Kokoro of the women. It starts with a soft kiss, then they taste each other's private parts and experience their first orgasms. The older brother suddenly appears and drills a sex education into the younger sisters, who are now obsessed with pleasure. The younger sister's complicated feelings are overcome by the pleasure and she approaches her brother with raw emotion.