Better yet, they act like an ethereal Cupid, going out of their way to mold unrequited crushes into something beautiful, whether honeyed romance, or pure carnal satisfaction.
Ethereal cupids. ...Or intentionally corrupting people by setting up liasons that are inappropriate. I brought this up at the Discord as well and think the funniest way to do this is if the victims get blurry memories and don't realise that they had been possessed when they had sex.
Twist: the ghosts actually loathe each other (as in, murderous hatred), and they possess a couple... yet find that the bodies categorically refuse to harm each other.