Hentai tells the story of a very complicated relationship between childhood friends Reki Shigen and Ayumu Matsuzono. They have been inseparable since childhood, killing time together and saving each other together. As time passed, the River grew into an incredibly sexy beauty, and Ayumu was weak and helpless, so he remained. Because of this, he often got into trouble, from which his girlfriend always helped him out. Once Ayumu got into a terrible situation – a group of villains grabbed him and decided to teach him a lesson. The river tried to protect its weak childhood friend as best it could, but the forces were unequal. Then they came to the aid of the brave karate Yamato-san, who saved our heroes with a couple of precise blows, which won the heart of the River. However, it was just a game… In fact, Yamato prepared a real punishment for Ayumu – he decided to fuck the River right in front of his eyes. Unsuspecting River gladly went to a love hotel with Yamato, and in the next room....