Guardians of the Far Frontier (manga)

An aristocrat named Ashath, has been assigned to a quiet post called the "guardian of the outer shell," a security force for the elite, far from the castle. Ashath was left behind after his unit was wiped out in a battle. Regretting his situation as the lone survivor, his dreams are full of nightmares of that battle.

He then meets Durant, a foul-mouthed sorcerer, who removes the nightmares with his magic. Durant also may be falling for Ashath