The Anime Lad
Kenji Koiso, an eleventh-grade math prodigy, agrees to a summer job at classmate Natsuki's family home in Nagano. She introduces the job after arrival: pretend to be her fiancé during a large birthday gathering. Then Kenji receives a strange numerical problem on his phone. He solves difficult equations more readily than social arrangements.
Super Eyepatch Fox
Natsuki brings Kenji to Nagano for a vaguely defined summer job. Her extended family is gathering for its matriarch's ninetieth birthday, and Kenji must pose as the fiancé nobody expected. A strange code reaches his phone while OZ connects much of ordinary life online. His mathematical talent suddenly matters beyond the reunion.
Gigguku
Kenji walks into a Nagano house full of Natsuki's relatives and learns that his summer job is fake-fiancé duty. That alone could power the visit. Then a mysterious math problem arrives on his phone, with the online world of OZ sitting behind it. I love the contrast between one awkward teenager, a huge family gathering, and trouble that begins as numbers on a screen.
Father's Basement
The idea that one online system controls nearly every part of life is convenient enough to show its wiring. Summer Wars gains credibility elsewhere. Kenji is trapped inside a specific family event before the digital problem expands, and his fake engagement creates pressure unrelated to technology. The human mess keeps the polished virtual premise from becoming an empty interface demo.
