Seigai no Majo

In fifteenth century Rome, witches have declared war against humanity. A young man named Nikola, whose parents were cruelly murdered by a witch before his eyes, discovers that he is now the key to winning the war. Using sorcery skills acquired through years of careful study, Nikola must revive twelve witches known as the “First Witches” who will become his allies and weapons to defeat the enemy. But there is one small hitch: in order to revive the witches from their eternal slumber, Nikola must form a marriage contract with each one. Just how many witches can Nikola marry in order to save the world?

(Source: Seven Seas)