goyuu

idk if you've played chaos;head (or watched it, I never saw it so idk if it's in the anime) but it's set in the same world as steins;gate (which I've watched but never played) and things the eyes see but the brain doesn't process are a literal plot point, you could almost certainly make a fairly lore accurate manip with that if you like this world.

“Good girl, sissy! I knew you had it in you! And now, you're about to really have it in you!” She laughed at her own joke, and started to push. True to her word, at least she went slow. I gasped and moaned, feeling the huge, hot weight of her gradually stretching me open, relentlessly forcing her way inside. She grabbed hold of me, one arm wrapping tightly around my leg, her other reaching around to grasp my dick. She wasn't stroking me anymore, not intentionally, but as she began slowly thrusting in and out of my ass, working her way deeper, the effect was the same. It took her maybe five minutes or so to finish getting all the way in, pressing hard against my ass, grinding to make sure I was feeling every last inch she had to give.

I swallowed nervously, but there was nothing else I could do. “Please, Ray...” I began, but at the tightening around her eyes I knew I'd made a mistake. “Please, Rachel... please give me your cock! Please, fuck me, Rachel! I want it! I want it so bad! I want your huge, thick eight inch cock up my ass!”