Once he went to his girlfriend's house to report, Nahoto was surprised to see her sister- Onee-chan appeared with a pajamas without wearing underwear to reveal the two nipples that looked very excited, making him fascinated from that moment. That night, after being invited to stay and used rice, while getting water for his girlfriend to see her again with the suggestive outfit at the beginning. This time he could not control himself, so he secretly peeked at a part of his chest exposed but unfortunately he was discovered. The lust began to rise, she constantly used words even sensitive actions like touching the penis, making him not know what to do but stand still to enjoy but forget to get water before. From here, he began to learn more about adults with the affair with her behind that poor girlfriend.