This Is the Wizard's Secret Weapon, Vol. 1 (light novel) — Taro Hitsuji

His strength is his greatest burden…and his greatest weapon!Rix, a master swordsman, is tired of bloody battlefields—so he fakes his own death to go into retirement! Seeking to turn over a new leaf, he enters a prestigious magic school despite having no magical aptitude whatsoever. Nonetheless, he’s ready to work hard alongside fellow scholarship student Shino, undeterred by her icy demeanor. Thanks to his skill with a blade, he over-whelms his peers, inadvertently steamrolling everything in the curriculum until he catches the eye of the imperial princess, Serephina. She wants to put Rix back on the battlefield, but he’s got other plans—become a wizard and live a fun and peaceful life!