Demonic Sorcery

Devan, a 16-yr old girl who was abandoned at the age of 5 tries to prove herself to the citizens of Rome but after failing several times she isolates herself in forest where she walks a path with a demonic source, the demon was convinced that she was worthy to wield the powers. Now with Demonic Sorcery and guidance from a retired warrior and a spirit she vows to protect Rome, but from what?