Mireille

A female knight who leads the guards, and is dedicating to protect the royal family from harm.
She is a warrior woman who trains hard and resides in the castle. She is calm, collected, and is an excellent leader. She is trusted by man from the royals to the knights.
She is only really good at swordsmanship, and is not well-versed in sex. Although she is a loyal knight, she is suspicious of the older sister, and pays close attention to her and the main character.
He finds it annoying and ends up raping her. But despite the humiliation, she remains rebellious and tries to cut the protagonist's neck whenever she can.