Chivalry of a Failed Knight(2013)

Rakudai Kishi no Cavalry

In a world where people with supernatural powers, called Blazers, manifest their souls as weapons, Kurogane Ikki dreams of becoming a Mage-Knight. It’s too bad he has no natural talent for it. The whole school ridicules him as the worst Blazer, so color everyone surprised when he suddenly defeats Stella Vermillion, a Rank A Blazer, in a duel. And so begins his fight to the top!

(Source: J-Novel Club)