Teenage math whiz Kenji Koiso agrees to take a summer job at the Nagano hometown of his crush, Natsuki. When he arrives, he finds that her family have reunited to celebrate the 90th birthday of their matriarch. His job: pretend to be Natsuki's fiancé. Meanwhile, his attempt to solve a mathematical equation causes a parallel world's collision with Earth.

Ryunosuke Kamikias Kenji Koiso (voice)
Hitomi Miyauchias Natsuki Shinohara (voice)
Mitsuki Tanimuraas Kazuma Ikezawa (voice)
Sumiko Fujias Sakae Jinnouchi (voice)
Ayumu Saitoas Wabisuke Jinnouchi (voice)
Takahiro Yokokawaas Takashi Sakuma (voice)
Kiyomi Tanigawaas Yukiko Shinohara (voice)
Mutsumi Sasakias Kazuo Shinohara (voice)
Mieko Nobusawaas Mariko Jinnouchi (voice)
Takuya Kirimotoas Riichi Jinnouchi (voice)