A demi-human cat-boy, Felix Argyle loyally served Duchess Crusch Karsten as her personal knight and attendant. Because of a promise involving Crusch and the late Prince Fourier Lugunica, Felix, who insisted on being called Ferris in all but the most formal of occasions, dressed and acted like a woman. Alongside the Sword Demon Wilhelm van Astrea, Ferris was a chief supporter of Crusch in her campaign to become the forty-second ruler of the Kingdom of Lugunica. Unlike the other men who served as the personal knights (except Subaru Natsuki) of the other candidates for the throne, Ferris was not a capable combatant worthy of defending his master. Instead, Ferris was a masterful healer, heralded as the greatest wielder of water magic in the Kingdom of Lugunica. Because of his skill, many people flocked to Ferris from all over in search of his medical expertise.