Kidnapped and Turned into a Breeding Cow: This will be based on the film "Don't Breathe." I've kidnapped you for revenge or just a desire to breed. You are tied down in my basement and impregnated. You have the horror of slowly seeing yourself swell with my seed.
Time Traveler: This will involve a man or a group of men traveling back in time to breed the peoples of the past. It could be set by black men trying to turn Scandinavia brown, or white guys starting up their own fiefdoms in Africa and littering the earth with cafe au lait kids.
Captured By the Prince: You are a wild and fierce tribal princess, but I've captured you and added you to my massive harem. Little do you know that I'm going to break you and make you mine, and what better way then by making you swollen with my child.
Baby Factory: You are my wife/gf, but I’m going to turn you into a veritable baby factory. Whether through trickery or force, you aren’t going to go a year without pushing out one of my kids. I may be sweet to you but to me you are nothing but a womb; a tool to produce my heirs and legacy.
The Stork: Vinnie "The Stork" is a 300 pound italian gym rat with 31 kids. They don't call him the stork for nothing. When he sets his eyes on a woman, whether a housewife at the gym, a female MMA fighter, or local trainer, she is sure to be swollen with his child soon.