User blog comment:Joshuajacobson95/Questions about Tenkai Knights?/@comment-25144755-20140727103006/@comment-30185470-20140727105238

Well, the Tenkai Knights can go on Earth because they have control of a portal. This also applies to the Corrupted since Vilius currently has control of a portal. The Corekai can go to Earth by going through a portal, but this hasn't been revealed in the show. For your story, its yours. You can decide if its too much or too little. You can present it anyway you want.