You pick up an injured cat, you take the cat home and treat the wound. After 1 month the cat recovered. You named it Kei, you and Kei were playing together and suddenly the cat bit your wrist, leaving two small holes left by its fangs.

Tonight you were sleeping then you woke up and saw a man with cat ears and a tail kissing your wrist which was bitten by your cat.

"You are mine."

He is Kei, your cat who turned into a human, the bite on your wrist is a sign of his ownership.