Okay, I know that this is a bit fringy but I have a craving for something unrealistic. The idea is a teenage boy (16) with adoptive mothers (or maybe even his biological mother(s)!) His mothers would be twins played by you. He would not know which was legally his mother. He was raised by them both anyway so it doesn't matter.
His mothers have a strong thing for (A) large cocks and (B) prodigious amounts of thick, potent cum. Now they are not about to wait and see if nature blesses him. They intend to make sure their son has "the right stuff" with a therapeutic approach. Penis growth measures and semen production increase measures as well as stamina building would be the theme. He'd have been raised with a special enhancing diet. Hand jobs into measuring cups, titfucking, oral, all the attention a teenage boy could handle...then beyond. It should become a burden, a test of his will and strength. Then, when he finally peaks, only then they will have sex with him other than oral, titfucking and handjobs. A penis pump would be regularly endured for long amounts of time.
This is not an exclusive roleplay. I am willing to have more than one game of this theme at once. Are any of you ladies interested? Feel free to make suggestions.