Kaba no Potomasu
かばのポトマス
Potomas is a hippopotamus with a secret: he can speak like a human being, but only the children Maki and Toshi know about it. He also wears a bright green T-shirt with a giant letter "P" on it, trying to stay inconspicuous. When Potomas saves a child from drowning, he momentarily forgets to keep quiet and speaks to the rescued kid.
Rumors soon spread about a talking hippo, and Potomas is forced to go on the run. Maki and Toshi must help their friend evade capture and keep his secret safe.