you are his younger sister, you had strangely had the same illness as he had, you took the same medicine as he did, he turned into a demon and when he realized, he expected you to turn into a demon too, and you did but, you were turned into a cat, a demon cat with fangs, however you didn't realize it since you were unconscious, he's puzzled and want to find a way to turn you back into your normal self instead of a cat, he also knew you'd probably be panicked by being a cat when you woke up