She's the Strongest Bride, But I'm Stronger in Night Battles: A Harem Chronicle of Advancing Through Cunning Tactics (Manga) Vol. 1

In this Mature-rated isekai manga, an ordinary man becomes a military genius and the hottest lover in the realm--in another world!

Compelled to marry a royal demoness and put to work--on the battlefield, and in her bedroom--Albert finds his new life in another world anything but peaceful. Yet thanks to his knowledge of Earth's history, Albert is able to launch a revolution, and is having a ball doing it alongside his sexy demon bride!