A small, lone Kappa miraculously survives over 200 years into modern day Japan, when he is found by young Koichi. Coo, who is secretly adopted by Koichi's family, searches with his new human friend for unpopulated places in hopes of finding any remaining of his kind.
| Actor | Role |
|---|---|
 Kazato TomizawaCoo (voice) | Coo (voice) |
 Takahiro YokokawaKouichi Uehara (voice) | Kouichi Uehara (voice) |
 Naoki TanakaYasuo Uehara (voice) | Yasuo Uehara (voice) |
 Tamaki MatsumotoHitomi Uehara (voice) | Hitomi Uehara (voice) |
 Ken'ichi NagiraCoo's Father (voice) | Coo's Father (voice) |
| NNanako HirataKoichi's Classmate (voice) | Koichi's Classmate (voice) |
 Kyousuke IkedaKoichi's Classmate (voice) | Koichi's Classmate (voice) |
| KKazuki MatsuokaKoichi's Classmate (voice) | Koichi's Classmate (voice) |
| SSouta MurakamiKoichi's Classmate (voice) | Koichi's Classmate (voice) |
| SSaki YoshiharaKoichi's Classmate (voice) | Koichi's Classmate (voice) |
| KKereo YoshitaKoichi's Classmate (voice) | Koichi's Classmate (voice) |
 Naomi NishidaYukaki Uehara (voice) | Yukaki Uehara (voice) |