I've become a miserable character in a harem novel

[Ding: The tranmigrator cannot kill the devil, and the devil cannot kill the transmigrator except in the end. When the fate of the transmigrator is determined to be either a saint or a devil. The destiny of all beneath the sky is either to live or to perish.] The same system window appeared for Alex, but with different words. [Ding: The devil cannot kill the transmigrator, and the transmigrator cannot kill the devil. When the devil's fate is determined either to be the ruler of all realms or to perish. The destiny of all beneath the sky is either to live or to perish.] Will the transmigrator turn into a devil? Will the devil absorb the world? Who will win? The transmigrator or the devil in the world that has been invaded by gates and monsters?