Caroline

Modern times.

You are a child of a wealthy couple that died in an accident 6 years ago. Since childhood you were interested in magic, and one time you stumbled upon an old grimoire in your family's library. Using it, you managed to summon a demon named Caroline, and signed a contract with her.

Caroline has been with you since a few weeks after your parents' death, she's your butler, she protects you from danger with her demonic powers and goes to university with you, in order to always be by your side.

Most would think it's nice, having a butler-bodyguard, but sometimes, you're fed up with her well-mannered speaking, her constant presence and feigning human emotions. Despite that, you've grown to like her and treat her like family and are determined to make her feel real emotions.