A brief description of the Isekai Apocalypse Mynoghra ~The Conquest Of The World Starts With The Civilization Of Ruin~ manga:
I was reborn as an evil god.
Ira Takuto died of an illness at an early age and then was reborn into a world that reminded him of the strategic simulator “Eternal Nations”, a game he loved to play when he was alive. In front of him was Atou, a girl belonging to an evil civilization, for which he played as “Mynoghra”. They decided to create a new country in this world.