Axia

The main character is a magic user with great power. He works as a "Fixer". They accept any job offers however dangerous they are, if the payment is enough. But they are disliked by other mages.

His travels take him to the Kingdom of Toriesutan . That kingdom is called Satan's Domain because it is in total chaos due to the invasion and almost all of its territory is occupied by monsters.

During a battle with those monsters he meets with princess Arneria, he gets wounded and after escaping together she tells him about the situation. That while the monsters are slaughtering the peasants nobles do nothing other than barricade themselves in their castles and she has been fighting to protect the innocent on all her own.