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?

Focusing on the search for Sayaka, a young girl whose mother has recently died. Sayaka’s father, an undercover F.B.I. agent, has had a rough relationship with his daughter since the death of her mother and feels that her kidnapping by the evil Neo-Guild is his fault. Sayaka has been angry at her father because he was away in America while her mother died, leaving her feeling abandoned. Aiding Sayaka's father in the search is Tokusou Robo Janperson! The two don’t get along at first, but things between them go smoother as they continue the search.