Felix Argyle, commonly known as Ferris, is Crusch Karsten's knight. Ferris has flax colored hair and yellow eyes. His casual wear consists of a blue collar with a ribbon, a blue dress, black tights, blue leggings, blue shoes, white arm covers, and a blue scarf tied around his right arm. Ferris' cat like features are a result of his mother having an affair as the rest of his family are all Human. The white and blue ribbons that he wears in his hair are a gift from Crusch and he always wears them no matter what he's wearing. .
Ferris usually refers to himself in third person, calling himself Ferri-chan, though he will refer to himself as Ferris, Felix, or with female pronouns depending on the situation. He is absolutely loyal to Crusch and will do anything she says, however he will oppose her if needed. He also enjoys teasing other people, especially those that are surprised that he's male, using cutesy language and gestures to agitate them. Although he hides it through his actions and words, Ferris has a severe view on death and values due to his job as a healer, leading him to hold those who no longer have any will to live in contempt from the bottom of his heart. He also hates weaklings because of his own complex, causing him to hate Subaru for a while, however he lets go of his feelings against him after seeing his actions during the battle against the Hakugei. Water Magic: Ferris is considered to be the best Water Magic user on the continent, earning him the alias of Blue. He is also the youngest to be given this alias. By directing mana to anyone whose Od he's interfered with, he can make their body go out of control, enabling him to do things such as using their body like a puppet or destroying their circulatory system from inside. He can also die and heal himself to perfect condition, as shown during the battle against Petelguese, however it is unknown how many times he can do this. Divine Protection Ferris has the Divine Protection of Water, which makes him highly skilled at Water Magic.