Summer Wars

Kenji Koiso spends his summer at the country home of Natsuki's enormous family after she asks him to pretend to be her fiancé for her great-grandmother's 90th birthday. While the shy math prodigy tries to survive the family's questions, a mysterious numerical puzzle arrives on his phone. He solves it overnight, never realizing that the answer has opened a door into OZ, the virtual world on which much of everyday society now depends.

A hostile program begins seizing OZ accounts and connected systems, turning an online crisis into real disruptions of traffic, communications, and public infrastructure. As the damage spreads, the family home becomes an unlikely command center. Kenji's mathematics will matter, but defeating an enemy living inside a global network requires something even harder to calculate: an entire family willing to stand together when the problem becomes larger than any one person.