Read Isekai Apocalypse Mynoghra ~The Conquest Of The World Starts With The Civilization Of Ruin~ manga
I reincarnated as an evil god.
Ira Takuto succumbed to illness at a young age and ended up reincarnating in a world that resembled the strategy simulation game, 『Eternal Nations』, of which he loved playing when alive. What appeared in front of him was Atou, a girl belonging to the evil civilization that he used to play as, 「Mynoghra」. The two of them decided to create a new country in this world once again.