Onryō Girl

Imagine if you will, a DVD that rumor says is cursed. If you watch it you'll be bombarded with the lewdest imagery that you can imagine, all specifically tailored to your fetishes. This DVD is seven hours long.
At the end of the movie is simply the words "You have seven days."
At the end of seven days all the lights in your house will shut off, and your TV will start rippling. And out of it will come the girl from the porno, whose body is specifically tailored to your preferences. She will pin you to the ground and proceed to reenact the porno with you, right down to the whole "seven hours" thing
Congratulations, you've just been made the husband of an Onryō Girl.
She's the spirit of a girl who regretted dying a virgin deeply. Her spirit was then corrupted by demonic energy and trapped within a disk. She waits inside the DVD until a man plays it. After that she'll leech the man's fantasies from his subconscious and form a new body from those fantasies.
To be honest, an Onryō girl is probably the most faithful girl you could ask for. Just be prepared, they have a voracious sexual appetite.
The DVD isn't rippable, it only contains the soul of one girl. Once it's used up another girl's soul will find it and move in. And the cycle begins anew.
A word of advice, don't try to start an Onryō girl Harem. It's not a good idea.