Hyppo and Thomas(1971)

Hyppo and Thomas is a classic anime about an unlikely friendship between a cunning bird and a gentle hippopotamus. Thomas, a scheming opportunist, lives inside Hyppo's mouth and constantly tries to outwit his good-natured host despite depending entirely on him. Their relationship is built on banter and conflict—Thomas acts superior while Hyppo remains patient and simple—yet beneath the squabbles lies genuine affection and cooperation. Created by Tatsunoko Production, the series finds humor in their mismatched personalities and the absurdity of their living arrangement, exploring how two very different creatures learn to coexist and support each other through their endless quarrels.