Forbidden Song

Ever since Yui first entered the Sakamaki household, she would frequently hear a piano playing throughout the mansion. Also, unexplained things kept on happening that would always interrupt one of the brothers from drinking her blood and hurting her. Yui came to a conclusion that God has finally answered her prayers and has sent a guardian angel to protect her...
However, what if this so called "guardian angel" isn't what Yui thinks it is?

I don't own Diabolik Lovers or any of the pictures that I've used :)