Hakofugu (Black spotted boxfish) lacks confidence and always stays alone by the rocks, watching other fish and feeling envious. Then, one day, upon meeting Himetatsu (Korean seahorse), who has lost the way and is said to be from the sea of Minamata, Boxfish's very first adventure begins. This film is based on the picture book "The Boxfish's Wish" (published by Kodansha), written by Sakana-kun (Fish Guy) — a Japanese marine biologist, TV personality, and illustrator.
| Actor | Role |
|---|---|
 Keiko TodaHakofugu (Black spotted boxfish) | Hakofugu (Black spotted boxfish) |
| AAmo YuikawaHimetatsu (Korean seahorse) | Himetatsu (Korean seahorse) |
 Hikari IshidaHimetatsu'mother / Bluefin tuna / Japanese sardine | Himetatsu'mother / Bluefin tuna / Japanese sardine |
 Masafumi KobatakeGreat barracuda /Moray eel / Japanese sardine | Great barracuda /Moray eel / Japanese sardine |
 Yu OkanoMarbled rockfish / Japanese sardine | Marbled rockfish / Japanese sardine |
| HHajime SugimotoHimetatsu's father | Himetatsu's father |
 Sakana-kunWhale shark | Whale shark |
 Tomomitsu YamaguchiAsian sheepshead wrasse / Japanese sardine | Asian sheepshead wrasse / Japanese sardine |
 Tsurube ShofukuteiCommon octopus | Common octopus |