Seek a very early Japanese anime, what happened on an island, but it is not an uninhabited island story.

according to your description, it may be the Japanese animation コナン (English name: Future Boy Conan) which was broadcast in 1996.

Based on the original story of the famous writer Miyazaki Hayao, this drama tells an adventure story that happened after the destruction of future civilization, and there is only one small island in the world. The story is tense and exciting, smooth and natural, and has been widely praised in Japan and around the world.

if you have any other information, please provide more details, and I can help you with your inquiry again.