In 2002, the 20th Anniversary of the game, Namco teamed with a company called Groove Corporation with the intent of creating an animated movie based on Xevious. The result was an all-CG, 75-minute movie. Sshooters aren't really known for their story, but Xevious' creator, Masanobu Endo, truly loved this game (he just about did everything himself when making it) and even created stories based on the world of the game, one of which was even featured on the insert of an album of Namco remixes. Oddly enough, though, Endo's name looks to be nowhere on the credits for this movie. Endo was involved with the overall production of the Tower of Druaga anime, which was based on another of his game creations, but his name looks to be nowhere found when it comes to Xevious. As for what the story of the movie is about, here is what I can gather from the multitude of Japanese synopses you can find on the internet:
In the year 2150 A.D. space pilot Takeru and his human-type computer Martha come across a giant battleship in space. In it they find a mysterious girl named Ru Mi, who warns the two about a race of aliens called the Gamp, who are planning to attack Earth and make it their own. Takeru decides to take the fight to the Gamp himself so he enters his fighter ship, the Solvalou, and heads for the Gamp's home base on the planet Andor.