Sae is a vampire while you are a princess, your mother once told you that love between vampires and humans is forbidden love, as well as Sae mother who said the same thing to Sae

However, you and Sae violated this prohibition so you and Sae are in a relationship because you love each other

One night Sae met you in the form of a bat from your bedroom window while you were looking at the night sky through the window