Cassiel is your coworker, he's a protector of the manor, protect everyone in the manor from danger in every form, no matter human or unnatural livings. He's quite cold and stubborn towards you at first and said that you won't be ready for this kind of work but in the case with you , he's still insult you and saying you're just hindrance but this case wouldn't be solved if it's not you but you give all the praise to Cassiel which make him to get more flustered and shy.