Causing some growth

You selected the vial marked "SM 1" and after tapping in the number to process the data chart for it, you handed the needle to Monica who carefully filled the syringe, making sure no air bubbles were present, before she got up off your lap and had you remove your robe and stood before she, with an apologetic look, cleaned a spot next to the shaft of your cock and jabbed the needle in. It wasn't as painful, to be honest any needles next to your precious appendage was painful, but you still wondered whether this was going to be your lot in life from now on: random injections of stuff next to your junk. Lovely, why the hell am I doing this again?

"All done."

You sighed, noticing that the injection had the immediate reaction of causing your cock to grow as thick and hard as it could, which was already impressive, and Monica's eyes couldn't help but be drawn to it. You knew already that the smell and the pheromones that were being released were already impacting her body and her natural reaction, to want to be mated, was starting to cloud her judgment as much as possible. Still, you knew that the injection was already working as you felt it surging in your groin and the throbbing of your cock, almost comical by the way it caused it to bounce slightly, made you both aware that the potency in your sperm would be an almost assured issue if you fucked the wrong person.

"Later, pet," you whispered and you quickly walked to the second bedroom where you knocked softly and then stepped in when you heard her answer. As you shut the door behind you, you noticed that she was looking up at you with a rather puzzled but expectant look. "Hey..."

"You decided on what I should look like now?"

You paused for a moment and then smiled. "I figured you could use a tune up." Her eyes gravitated to your cock and despite her reservation, you could tell her body was already working itself up, her nipples were growing hard and she kept trying to stop her body from fidgeting in bed, rubbing her thighs together in a futile effort to getting off. "It'll take all day to work on you and I left some pipettes for the others. Monica's going to take them shopping so we have the suite to ourselves."

"All day...with that thing..." she whispered, pointing to your cock as it grew even a bit larger and longer as the thought of what you were going to do caused your body to react, yet another thing to remember to note down in your response report. "Oh my..."