Kazuma Ikezawa (池沢 佳主馬 Ikezawa Kazuma?) - The 13-year-old cousin of Natsuki Shinohara. His avatar is King Kazma, a renowned martial artist in the World of OZ. Kazuma is also a hikikomori who seldom leaves his room and uses his talents to win every game in OZ. But it's hinted that he does have friends, as more a spin-off manga made after Summer Wars telling about how he was able to become King Kazma. When he is not in his room, he trains in Shorinji Kempo with his grandfather, Mansuke Jinnouchi.
His appearance involves tanned skin, short black hair with bangs that cover his right eye. His eyes are a dark brown, nearly black, color. He is very short for his age. He's seen mostly with headphones around his neck or on his head and in front of a computer playing OZ.
Kazuma makes his first appearance when Kenji Koiso wakes up at night and searches for the bathroom. He stumbles upon Kazuma in his room, on his computer. Kazuma then directs him to the bathroom. Kenji asks if he will join the others, but Kazuma ignores him and goes back to typing something.
The next day, after Kenji solves the number puzzle he is given the night before, he panics and flees to Kazuma's room. He lets Kenji use his computer to log into OZ and they soon discover that Kenji's account has been hacked. Takashi Sakuma lends Kenji a powerless avatar to confront the mysterious hacker. The hacker, actually an AI called Love Machine, begins to attack Kenji. Annoyed, Kazuma takes over again, switching to his famed avatar, King Kazma.
Kazuma is seen typing rapidly as Kenji stares, open mouthed during a fierce battle between the AI and King Kazma. When Kenji tries to talk to Kazuma, he tells Kenji that he can't concentrate if Kenji is talking. Eventually, King Kazma captures Love Machine and holds him captive in front of the rest of OZ. Suddenly, Yuhei and Shingo Jinnouchi tackle Kenji, causing Kazuma to lose his focus on the game. Love Machine slips away and eats two spectating avatars, making his character bigger and stronger. The two continue fighting until Love Machine proves too much for Kazuma and King Kazma is defeated.
Later on, after Sakae Jinnouchi passes away, Kazuma and a few others devise a plan to capture the AI. An overwhelming amount of materials are brought to maintain the computer, including several huge blocks of ice. For the second time, King Kazma battles Love Machine and traps it in a building that is filling with water. Just then, the computer system overheats as Shota Jinnouchi had taken the ice blocks and put them near Sakae's body. Kazuma loses his temper and punches Shota, and it takes a lot to restrain him from doing so again. Love Machine breaks free, absorbing almost all the avatars and turning into a black mass. Kazuma continues to attack, but his avatar is soon grabbed by the AI as well. Kazuma, who has begun to cry, says, "I'm sorry I let you down."
In the final battle, Kazuma's avatar is pulled back to his feet and, while Natsuki is battling the AI in Koi-Koi, defeats Love Machine once and for all.