Theatrical movies, or gekijouban (which translates roughly as "Theatrical Edition"), based on popular manga aren't anything new, and that counts even more for Shonen Jump anime. Naruto and One Piece, for example, have their fair share of movies (One Piece is at 10 as of this writing and I don't even bother to keep count of all the Naruto movies), and Dragon Ball has an insane 17 movies, four from the original series and a whopping 13 from DBZ (and GT has a movie as well, but I don't think it was theatrically-released). So, naturally, Saint Seiya has a series of movies to its name, five to be exact, and most of them have kind of become forgotten as time went on. For those who are unfamiliar with Saint Seiya, the basic idea is that there are warriors called Saints who fight for the sake of Athena, goddess of wisdom, primarily Seiya, the Bronze Pegasus saint, and his friends, who fight to protect Saori Kido, who is the present human reincarnation of Athena.
Saint Seiya (Gekijouban) debuted in July of 1987, and has since become more known as Saint Seiya: Evil Goddess Eris. The TV series was only about one-third of the way through its airing when this movie debuted, and like most movies of this type its canonicity can be debated. In this movie we're introduced to Ellie, a girl who helps out at the orphanage that Seiya and Miho live at (Remember Miho? You know, Seiya's sort-of love interest?). One day she sees a young orphan run into the street and she goes after him, but before they're hit by a car Cygnus Hyoga saves them and the two start to fall for each other. One night the two see a shooting star and Ellie is entranced by an object that broke off of it, which Hyoga doesn't notice. Upon finding it Ellie is possessed by Eris, Goddess of Chaos, who promptly kidnaps Saori/Athena and reveals that she will drain Athena of her powers by using the Golden Apple of Greek Myth. In order to make sure that the Bronze Saints don't stop her, she revives five dead saints with new bodies and calls them her "Ghost Saints": Shield Yan, Sagitta Maya (not be confused with the canonical silver saint Sagitta Ptolemy, who had not debuted in the anime at this point yet), Lyra Orpheus (who would be altered somewhat and re-used in the actual story much later on as Lyra Orpheé), Southern Cross Kristos (yes, his name is essentially Christ), and Orion Jager.