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 Kamiki
as Kenji Koiso (voice)
Hitomi Miyauchi
as Natsuki Shinohara (voice)
Mitsuki Tanimura
as Kazuma Ikezawa (voice)
Sumiko Fuji
as Sakae Jinnouchi (voice)
Ayumu Saito
as Wabisuke Jinnouchi (voice)
Takahiro Yokokawa
as Takashi Sakuma (voice)
Kiyomi Tanigawa
as Yukiko Shinohara (voice)
Mutsumi Sasaki
as Kazuo Shinohara (voice)
Mieko Nobusawa
as Mariko Jinnouchi (voice)
Takuya Kirimoto
as Riichi Jinnouchi (voice)