Zetsurin Kenja to Himitsu no Keiyaku

A world where people live in fear of magical beasts... Nobles with magical powers are known as "noble sorcerers" and they use their magic to destroy the beasts. Stella, the only daughter of Count Norris, should have died after marrying the violent Ethan Elliott and being locked in his cellar. But when she opened her eyes, she had returned to the day when her engagement was decided. To avoid facing the same future, she ran away. She then met a man named Lucas in the forest. Although Lucas is the son of Count Bloodrare, he is called incompetent because he is unable to use magic and is rumored to be impotent as well, because he does not physically react to any woman. Lucas cannot rejuvenate his magic on his own, but he recovers a little of it when he touches Stella, something that has never happened before no matter what he tried. In order for Lucas to recover his magical powers and for Stella to be free, the two enter into a year-long contract marriage. However, each time they come into contact with each other, they start to become attracted to each other, and they finally cross the line. Then, after recovering a great amount of his magical power, Lucas finally awakens his true power... (Source: POCKET COMICS)