Arthur de Richemont

Arthur de Richemont is one of the main characters of the Ulysses: Jeanne d'Arc to Renkin no Kishi light novel and the main protagonists of the anime series. She is the Princess Knight of the Principality of Brittany located in the northwestern part of France. She is also one of Montmorency's childhood friends, and the young boy's secret love since when they studied at the Knights Academy.

When the French army is wiped away in the battle of Azincourt, her broken sword has been found on the battlefield by Montmorency, pursuing the boy to think her dead. However it's later revealed that she's been captured by the English.

(Source: Ulysses: Jeanne d'Arc to Renkin no Kishi Wikia)