Summer Wars

Kenji Koiso is a shy eleventh-grader and gifted mathematician who agrees to spend the summer at the Nagano home of his older schoolmate and secret crush, Natsuki. Only after arriving does he learn the real job she has in mind: pretend to be her fiancé during her family's gathering for matriarch Sakae Jinnouchi's ninetieth birthday.

While trying to maintain the deception, Kenji receives a mysterious mathematical problem on his phone and cannot resist solving it. His answer unexpectedly contributes to the hacking of Oz, a digital system integrated into nearly every part of daily life. With the crisis escalating, Kenji and the enormous Jinnouchi family must work together to stop the damage.