Love Machine is the main antagonist of Summer Wars.
It is shown when he defeats other avatars that a pop-up will appear under their K.O. point, this pop-up lists the rules of the OZ martial arts mode and it can be briefly seen that players have agreed to "not use cheats or hacks to win", Love Machine, however, has hacked into all of OZ simply for his enjoyment and to cause chaos, meaning that he has severely broken the rules and does not care.
In his main form, Love Machine is a tall, strong-looking character with a black face, evil grin, pointed chin and deeply sunken eyes. He also has a large "crown" atop his head with 4 gold horns, a heart located in the center and a white egg-shaped piece to top it all off. He has various black markings along his body which appear to conduct his energy at times. Lastly, he has puffy black pants with an orange piece hanging down from his waist. He also clearly wears no shoes possibly to enable easier and more mobility.
Love Machine's insatiable thirst for competition appears to be is his only weakness. Love Machine is also said to love competition and games (particularly winning them) he is sadistic to some degree and though may have a programed "conscious" he does not feel remorse or regret for his actions, this is demonstrated when he uses accounts for his own purpose and attacks various avatar bystanders. As Love Machine hacked into all of OZ he has complete control which explains why he was not banned or deleted.
Love Machine is Artificial Intelligence (A.I.) created for the United States Government to use against enemies. It was created as a hacking program, but when it is released into OZ, Love Machine starts taking over other avatars and hacking into the main processor of the virtual world and his attempt at using the governments own missiles and weapons to wipe out others that stand in his way. Wabiskue describes Love Machine as an AI with a desire to learn. Love Machine sees everything as a game and plays them out like a game, devastating opponents and being swayed into other contests, such as the Koi-Koi rounds against Natsuki. It also gains power by consuming other avatars, becoming a far larger and more intimidating force. Kenji Koiso is a moderator of OZ, a massive virtual reality program, who is invited to the home of a friend Natsuki to celebrate her great grandmother Sakae's birthday. He receives a mathematical code in an email and cracks it, unleashing a malignant Artifical Intelligence called Love Machine. The AI hacks into Kenji's account and uses his avatar to wreck havoc on OZ's infrastructure. It is confronted by King Kazuma, the rabbit avatar of Natsuki's cousin Kazuma. Love Machine devours some unfortunate avatars and, in its new and bigger state, defeats King Kazuma in battle. It then attacks and gobbles up more avatars to increase its growth and power, hacking into other accounts. Love Machine causes more drastic effects in the real world by creating traffic congestion and interfering with electric devices. For a time, OZ is restored while the truth of Love Machine is revealed. It had been created by Natsuki's relative Wabisuke as a test run program and was sold to the United States military. Love Machine ultimately kills Sakae by cutting off her heart monitor, thus leaving her to die without anyone finding out before it is too late. Determined to defeat Love Machine, Kenji and Natsuki's family bring together a supercomputer cooled by blocks of ice. They manage to capture Love Machine but are thrown off when the supercomputer overheats, allowing Love Machine to engulf King Kazuma and gain more power. Using its power, Love Machine directs a satellite with the intent of crashing it into a nuclear plant. Finding out that Love Machine sees everything as a game, Natsuki confronts the AI in Koi-Koi rounds. While initially winning, Natsuki almost loses her winnings with the wagered accounts put up against Love Machine. Fortunately, OZ users all over the world put forth their support, giving Natsuki the chance to devastate Love Machine. Unfortunately, a spiteful Love Machine redirects the satellite to crash into their home. Wabisuke counters his creation by disabling its defenses, permitting King Kazuma to reconstitute. King Kazuma is led by several of the family's avatars and attacks Love Machine with a punch to the face, destroying it. Kenji manages to redirect the satellite from crashing into the estate (although its collision causes a geyser to erupt).