Chou Bakumatsu Shounen Seiki Takamaru (1991)

Within Japanese territory, there is an island that calls itself an independent country called the "Champon Kingdom," and it is still closed to the outside world. As a developed nation, the Japanese government, in an effort to force them to open up as soon as possible, sends Foreign Minister Fukuda and his son, Claude, to this strange island. (Translated)