This is my ideas,
1. A Futa (herm) and her lover (normal) decide to make a family. The Futa ends up making love to her pregnant lover, finding it to be her hidden fetish she has. After the first child she turns her lover in to a baby making machine.
2. Neko, a little neko is bought for her rare breed; her master/mistress breeds her to make kittens, knowing they will sale for a lot of money.
PM me and we can talk.