Unhappy after his new baby sister displaces him, four-year-old Kun begins meeting people and pets from his family's history in their unique house in order to help him become the big brother he was meant to be.
| Kun (voice) | Moka Kamishiraishi |
| Mirai (voice) | Haru Kuroki |
| Father (voice) | Gen Hoshino |
| Mother (voice) | Kumiko Aso |
| Mysterious Man (voice) | Mitsuo Yoshihara |
| Grandmother (voice) | Yoshiko Miyazaki |
| Grandfather (voice) | Koji Yakusho |
| Young Man (voice) | Masaharu Fukuyama |
| Baby Mirai (voice) | Kaede Hondo |
