Kore ga Mahoutsukai no Kirifuda

The master swordsman Rix, who has grown well and truly tired of the bloodstained battlefield, fakes his death in battle and retires. He has decided to turn his life around and enroll in the Magic Institute, despite having zero magic aptitude. Nonetheless, Rix is able to overwhelm the sorcerers with his base skills as a swordsman! Unintentional as it may be, he continues to smash through all common sense within the institute. In doing so, he catches the Empress’s eye, drawn to that battle prowess of his— Wait, no! I'm telling you that I'm not aiming to be the strongest or anything like that! What I want is a "peaceful and happy life"!

(Source: Kadokawa, translated)