A math-savy, 17-year-old high school student and a moderator of the interactive computer world OZ along with his close friend, Takashi Sakuma. Kenji is less skilled in dealing with people. Kenji is invited by his friend and girl of his dreams, Natsuki Shinohara, for Sakae Jinnouchi's 90th birthday. Only to find out he will be playing the part of her fake fiancee for the family reunion. He enjoys his stay and after the first night of being there, he receives a cryptic code on his cell phone and cracks it. Not knowing that it was the encryption key to Oz's security system. He is framed for the destrustion of Oz and is arrested, but is brought back to the house to fix what he had done.
He befriended the creator of King Kazuma, Kazuma Ikezawa, who is the Martial Arts champion in Oz. Together they attempt to defeat Love Machine in a one-on-one battle but lose. Kenji is grief strucken by Granny's death because the night before he promised her that he would take care of Natsuki.
Kenji wants to avenge Granny knowing that she could have been saved if Oz was operational. He and the men of Natsuki's family all work together to build a supercomputer to take down Love Machine, but their attempts to trap it, fail and King Kazma is devoured by Love Machine.
When Natsuki challenges Love Machine to a game of Koi-Koi he bets his avatar if she lost along with twenty other belonging to Natsuki's family. When Love Machine is defeated, the AI commands the satellite to crash into Natsuki's house, but Kenji breaks through the system three times to swerve it off path, thus causing him to have a nosebleed because he solved the last code in his head.
When everyone is safe they celebrate granny's birthday and Natsuki kisses him on the cheek, and he has a major nosebleed causing him to pass out. In the end he kept his promise to granny and became Natsuki's real boyfriend.
Polly Possum Created By Kenji Koiso