So, I was just remembering this little sex humor comic: http://ghastly.keenspace.com/d/20010509.html And suddenly this weird little idea popped into my head. A story about tentacle monsters... FEMALE tentacle monsters: trying to seduce human men. Other than a tentative motivation, (they're trying to figure out why so many males of their species are into human women...) that's all I've got. Anyone wants to grab this and do something with it go ahead: provided that if it's something rapey, you never tell me about it.
I don't know if this helps, but in the Russian culture(of which I'm vaguely part of) there's a monster called a Rusalka (руса́лка.) Russian culture would roughly translate it as a mermaid, but it's more accurate to call it a kind of underwater succubus. The account varies of what exactly they are, but the way I heard is they change shape to appeal to men, though in most accounts, they are never able to completely shift all parts of their body. The way I heard it was that they can't even completely leave the water, but not all stories tell it like that. There's the thing called Rusalka week where swimming isn't allowed in some places because of the belief that these things are most active and they will kidnap swimmers. So I don't know if there is anything there to work with. It just got me thinking about it. They aren't considered inherently evil creatures in most accounts(not all), that used to aid in fertilizing in crops. Maybe a story about swimmers who get too close to the water? Dunno.