Kujira no Josephina

Santi is a shy Spanish boy who keeps a tiny whale in a bowl, invisible to everyone but him. The whale, named Josephina, is able to alter her size and fly; she takes Santi on many dreamlike adventures and helps him confront the challenges during his childhood; however, things change as Santi starts taking interest in the outside world and gets to know his distant father.

Based on Adios, Josefina (Goodbye, Josephine) by Jose Maria Sanchez-Silva.

(Source: AniDB)