Seventeen-year-old Tenchi Masaki grew up hearing stories about how his ancestor used a sword to seal a demon inside a cave seven hundred years ago. When curiosity gets the better of him, Tenchi goes to the cave and stumbles across the sword from the legend. Thinking that the story is nothing more than a fairy tale, he removes the blade and inadvertently releases the demon, who turns out to be a space pirate named Ryo...