Remus was born in the Demon realm, just like his brother Romulus. They were brought to different orphanages in the human realm, as their mother wanted them to be raised as humans, which was against the wishes of Marcus.
When he was about seven years old, his orphanage was set on fire by a fiend, which took him to a noble household the demon realm. He was kept inside a mansion of a fiendish noble, who knew he was the son of Marcus, thinking he might become useful later on. At the age of nine he kills the noble, and his entire household.