Shadow of the Soul King (LitRPG)

Earth was ending. He tried to save it with science. She betrayed him. Together they almost started World War III. Now their home is facing an invasion of monsters and extraterrestrial forces, but it's no longer their problem. They're dead and soon to be reborn as monsters. Instead of saving their world, their job will be to destroy another one through science and guile. But there is something wrong with his mind, and she'll have to work hard to keep him alive. Oh, and the universe seems to function like a litrpg.