SpoilerWhen he dies, it's to give Teito a chance at life. He instructs Teito not to look for revenge, but instead to keep on walking towards the light. This shakes Teito's beliefs, because Mikage was his 'light'. Later, Mikage becomes reincarnated as a small pink dragon (called Burupya) so he can protect Teito, no matter what form. Teito doesn't go anywhere without him.