In Order to Marry the holy lady Wife, I had To defeat the Devil

[Single heroine + black belly + kendo genius + daily life (probably) + love + adventure + light novel] Leo, the inheritor of the ancient swordsmanship school, went down the mountain to join the world in order to save the declining kendo gym, and entered the whole continent as a commoner In the famous aristocratic academy, he wanted to keep a low profile and met his destined other half in the academy. In order to marry his wife, he was forced to embark on the road of defeating the devil and saving the world. (Slow pace, the hero and heroine didn’t like each other at the beginning, and gradually deepened their relationship as the plot progressed.)