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.
| Kenji Koiso (voice) | Ryunosuke Kamiki |
| Natsuki Shinohara (voice) | Hitomi Miyauchi |
| Kazuma Ikezawa (voice) | Mitsuki Tanimura |
| Sakae Jinnouchi (voice) | Sumiko Fuji |
| Wabisuke Jinnouchi (voice) | Ayumu Saito |
| Takashi Sakuma (voice) | Takahiro Yokokawa |
| Yukiko Shinohara (voice) | Kiyomi Tanigawa |
| Kazuo Shinohara (voice) | Mutsumi Sasaki |
| Mariko Jinnouchi (voice) | Mieko Nobusawa |
| Riichi Jinnouchi (voice) | Takuya Kirimoto |
| Rika Jinnouchi (voice) | Sakiko Tamagawa |
| Mansuke Jinnouchi (voice) | Ichiro Nagai |
| Tasuke Jinnouchi (voice) | Takashi Kobayashi |
| Shota Jinnouchi (voice) | Yutaka Shimizu |
| Naomi Miwa (voice) | Kaori Yamagata |
| Kiyomi Ikezawa (voice) | Tagame Tamura |
| Mansaku Jinnouchi (voice) | Tadashi Nakamura |
| Yorihiko Jinnouchi (voice) | Yoji Tanaka |
| Kunihiko Jinnouchi (voice) | Hashiya Nakamura |
| Katsuhiko Jinnouchi (voice) | Mitsutaka Itakura |
| Noriko Jinnouchi (voice) | Eiko Kanazawa |
| Nana Jinnouchi (voice) | Chigusa Takaku |
| Yumi Jinnouchi (voice) | Riisa Naka |
| Ryohei Jinnouchi (voice) | Naoto Adachi |
| Yuhei Jinnouchi (voice) | Rikito Ota |
| Shingo Jinnouchi (voice) | Yuki Imai |
| Mao Jinnouchi (voice) | Sumire Morohoshi |
| Kana Jinnouchi (voice) | Hinano Minagawa |
