Billy Galet is a childhood friend and love interest of Yuri first mentioned in "Gotta Do It! Love is a Woman's Detonator". Twelve years before the beginning of the series when Yuri was seven, he made a promise to her that they would travel across the stars together when he finished his ship named Lucia which then would have lead to them getting married. Instead during his adulthood when he became an engineer he was kidnapped and taken to a prison on Poisonville where he along with many other engineers were forced to build a space battleship full of advance weaponry. Apparently at one point Billy died and Kei discovered that all that was left was a transmitter in his locker with a locket on it that has a picture of Yuri when he knew her as a child and that he still loved her. Kei didn't tell Yuri that he was dead and Yuri might still has the belief that he may still be alive and working on Lucia but decided that she feels that wouldn't want to see him just yet anyways. The only time Billy is seen is on a picture that Yuri has in her locket of him as a child.