Magican from a monster invasio world transfered into a different world

A mage from a world where there are after a calamity and awaganing of magic regular monster invasions. is Transported into a different world.
He was one of the first mages and was one of the first mages to fight monsters. At that time it was a losing battle and majority of humanity was destroid. After the battles he becam numb to death and is activly fighting on the front lines in close quarter combat and can struck of normal rifle fire as if it was noting.
He is used by high command as clandestine operator that purges roge mages and a wild card to turn losing battles into victoris.
Now that he is strandet in another world he is relased from his duties and can life how he wants.