Kenji Koiso

Kenji Koiso is the main protagonist of the 2009 anime film Summer Wars. He is a 17-year-old student at Kuonji High School and a math genius. One day, he is invited by his friend Natsuki Shinohara to her great-grandmother 90th birthday where, much to his shock, he is to pretend to be her boyfriend. As he struggles to fit in, he receives an e-mail with a mathematical problem. After he cracks it, he discovers that his account has been hacked by a mysterious AI named Love Machine. Before he knows it, Kenji, Natsuki and her entire family are caught up in a battle that will determine the fate of the entire world.

He is voiced by Ryunosuke Kamiki in the Japanese version and Michael Sinterklaas in the English version.