During a visit to his girlfriend's house to work on a report, Nahoto was surprised to see her older sister - Onee-chan appear in a nightgown without underwear, revealing her breasts in a very enticing way that captivated him from that moment. That evening, after being invited to stay for dinner, while getting water for his girlfriend, he caught sight of her sister once again in a seductive outfit no less alluring than before.SSNI-751 Sister...I'm happy! This time, unable to control himself, he discreetly stole a glance at her exposed cleavage, only to be caught by her. The lust began to awaken, as she continuously used explicit language and even sensitive actions like touching his penis, leaving him unsure of what to do other than standing still and enjoying it, forgetting about getting water earlier. From then on, he began to learn more about adult matters through secret affairs with her behind the back of his pitiful girlfriend.
