Kaibutsu-kun (1968)
Original title: 怪物くん
Kaibutsu-kun is a 1968 Japanese-language animation series. It stars Fuyumi Shiraishi, Hiroshi Otake and Masao Imanishi.
The prince of Kaibutsu Land, Kaibutsu-kun, decides to go to the human world as part of his training to become the King.