There is a war between Vampires and Succubi. One girl holds the key to give either side a distinct advantage, and you just married her. How did you ever get yourself mixed up in such a mess? You will find the Succubi and Vampires are generally not nice to ordinary mortals.
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