Rebirth and Return from Another World

He came out and traveled to a place where there was a war in another world. Really, when he thought he was going to die, the system suddenly appeared and said, you have to become the enemy of this world, otherwise you will die. Will you? Will this end for the male protagonist? Impossible, he accepted it in his heart. This is my first book. I hope everyone will read it carefully and don't make random comments. This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.