In space, Ultraman Cosmos is battling with Baltan to stop him from invading Earth. A young boy named Musashi (Kounosuke Tokai) who is a 5th grader has a lot of dreams, such as becoming an astronaut to sail the sea of stars, and to meet Ultraman. One night, Musashi went to the forest to observe an eclipse with his friends. Unfortunately, that night, a heavy rain fell that made everybody decide to go home except for Musashi. Meanwhile, in the middle of that rain, Ultraman Cosmos is battling with Baltan to stop him from invading the city. They both use their powers and clashed at each other. Due to the impact made by their power clash, both of them were thrown into different directions.

In the years before World War II, a penniless Japanese child is torn from her family to work as a maid in a geisha house.