Another saiyan escaped the explosion of Planet Vegeta. Though this Saiyan landed on Equis (Pre-NightMare Moon Banishment). Luna finds Kale and decides to take him in and care for him as her own. She has to keep this alien warrior child a secret from Celestia however, or Celestia may think he's too dangerous to have around...
(http://vignette4.wikia.nocookie.net/dragonball/images/c/c5/Heroe(DBH).jpg/revision/latest?cb=20110316185157 Basic Look of Kale)

(Also, sorry if the prologue and the first chapter are a bit...rushed. Nothing else will be rushed)