A Growing Addiction
Some things cannot be stopped once started.
Chapter 1
by 
Gabidy-Gook
John before all this was just a normal horny guy, never suspecting that his life might change so drastically while away at college. Never suspecting that something, someone, or whatever bestowed this power on him would do so without him knowing. What is this power? Let me tell you:
John will jerk off to a girl and she'll put on some weight, if he jerks off to her again she'll put on more, even more than last time. The effect gets stronger every time he does it. Additionally his cock and balls will slowly grow as well, not even noticeable at first but soon it will be undeniable.
The girl(s), after him making them grow, will start to become attracted to John. Only slightly at first, just being friendlier, then become more overt, flirting and being suggestive, then finally being open about their attraction, in whatever form that takes.
All of this will make it so John will be more and more unable to resist masturbating further, making sure the women around keep getting fatter and hornier.
The only question left, is who does he discover this power with?