サマーウォーズ

Kenji Koiso is a high-school math prodigy who takes a summer job he does not fully understand: Natsuki Shinohara hires him to pose as her fiancé at her great-grandmother Sakae's ninetieth birthday in Ueda, in front of the whole Jinnouchi family. That night a string of numbers arrives on his phone and he solves it for sport, and by morning the accounts of OZ, the virtual world most of daily life runs through, are coming apart. This manga adapts Mamoru Hosoda's film.