Corrin has lived within the Northern Fortress for as long as he can remember. Now as Corrin is thrust into the outside world, he will discover forces beyond anything he could have imagined and a plan thousands of years in the making. A crossover between the world of Fire Emblem Fates and Shin Megami Tensei: Nocturne.

A year after Lyn, Eliwood, and Hector slew Nergal and foiled his plans to take control of the dragons, a mysterious figure appears in Ostia. Who is he, how did he arrive there, and what is the source of his frightening power?