During a visit to his girlfriend's house to do a report, Nahoto was surprised to see her sister Onee-chan appear in pajamas without any lingerie revealing her two stimulating-looking nipples that made him fascinated from that moment. That night, after being invited to stay for dinner, while going to get water for his girlfriend, he came across her again in an equally erotic outfit at first. This time, he couldn't control himself, so he secretly peeked at a part of his exposed breasts, but unfortunately he was discovered by her. Lust began to rise, she constantly used words and even sensitive actions such as touching the penis, making his cock not know what to do but stand still and enjoy it, forgetting to get water before. From this point on, his cock began to learn more about adulthood by having clumsy love affairs with her behind the back of that poor girlfriend.
