Musashi is a 10 year old boy with big dreams. He wants to grow up to be an astronaut so he can fly through the stars and meet his hero Ultraman. His mother worries that Musashi daydreams too much, but his police officer father thinks a little bit of daydreaming never hurts anyone.

Once again, Musashi has encounter Ultraman Cosmos. Now Ultraman Cosmos has gained some new modes to defeat Scropis. Musashi has joined Team Sea to save the Blue Area. But there is mysterious evil monster, Sandros, who wants to destroy the Earth. Now it is up Musashi and Ultraman Cosmos to defeat Sandros and who’s the other Ultraman?