Life has been tough for you as a half vampire. First, your human mother and vampire male caretaker are killed when you're still fairly young. But it brings you closer to the human sisters Valentine and Camilla who have been your friends since you learned how to walk. Especially with the two girls losing their own mother not long after yours.
In order for you to be able to install this game, you need to enable (allow) installation of applications from unknown sources (Unknown sources) in the phone settings. Usually this item is in the Security section