Maou No Utsuwa

Maou No Utsuwa summary:

A world of magic and swords.
Born into an aristocratic family of a large country, a boy with insufficient magic power bade farewell to his unlucky daily life. Because of his encounter with a Demon, his fate began to change. This destined meeting changed the boy’s life, affected his surroundings, and soon after, shook the entire world.
This is his tale.
[Description from NU]