Yuusha-sama no Oshishou-sama

Yuusha-sama no Oshishou-sama, The Master of the Brave novel:

After losing his parents, he yearns to become a Knight, the poor boy Wynn Byrd diligently train himself. However, it was hopeless for him to become a Knight, because his magical power was low, he can’t pass the Knight examination so he was labeled with the unpleasant title of 『Eternal Knight Cadet』. But one day the Brave defeated the Maou and saved the world. The Brave was a peerless bishoujo and she became the center of attention from the entire world. However, the Brave declared to the entire world. 「I will return to my Master’s side, Wynn Byrd.」 This is the story about a boy who somehow changed his class from 『Eternal Knight Cadet』 to 『Brave’s Master』.