Hippo and Thomas(1971)

Kabatotto

Thomas is a cunning bird who sponges on Hyppo, the good-natured hippopotamus. Although Thomas is a dependent, living in Hyppo's big mouth, he always acts lordly and tries to outsmart his simpleminded host. However, their basic friendship and cooperation endures despite their frequent quarrels. The two play a prime role in this comic series, short yet full of originality.

(Source: Tatsunoko website)