Nintendo describe Shin Megami Tensei X Fire Emblem as an RPG involving a struggle between “the worlds of glamour and darkness”. In the game, you play as “Mirage Masters,” who have big dreams of becoming great entertainers. They polish their singing and acting skills in the entertainment business in their daily lives, working their way up in the world as artists.
Meanwhile, there are “Mirages,” who are beings of immeasurable power that come from another dimension. They’ve begun to invade the world, and some of them are evil, while others are drawn to humans with tremendous creative potential, and have shared their powers with them to safeguard humanity. This is probably why the main characters are called Mirage Masters.
http://www.siliconera.com/2015/06/16/shin-megami-tensei-x-fire-emblem-story-details-from-e3-2015/