"I'll fap it out! If I cum, whatever's in there is going to get forced out by my jizz..."
Kim began fapping in earnest. She wasn't an especially petite girl, but her hand barely reached halfway around her massive anaconda even when it was soft, and her cock swung around like an escaped firehose. If you'd still been in the end of her cock, maybe you'd probably have been killed by the g-forces involved.
As she continued fapping, her floppy cock slowly grew harder and harder, soon reaching full mast and making Kim feel good as she yanked on it. You must have been somewhere near her balls, and with every thrust of her hand, Kim rammed her fist into you. It wasn't painful to her, but to you it felt like you were being crushed with each stroke as your big sister furiously fapped away, hoping to make you blurt out of the end of her dick.
It was hot and wet in there, and the only sounds you could hear were your sister's rapid, powerful heartbeat and her rapid, powerful fapping. You had no idea what was going to happen to you; were you going to be imprisoned at the junction of your big sister's cock and balls for the rest of your life? Were you going to be pulled into her testicles? Were you going to be shot out of her cock like a cannon?
Kim, seeing her reflection in the mirror, was fapping herself into a trance. By now, she couldn't feel whatever it was any more, and dedicated herself to fapping away while staring into the eye of her giant cock as it seemed to look back at her. She kept fapping, harder and harder, faster and faster, until you felt something new, a pulsating sensation. Kim braced herself, pointing her cock at the mirror and fapping even harder still. As her genitals throbbed, you prayed that you wouldn't be crushed to death in there.
Within seconds, Kim finally came. She came long and hard, shooting huge ropes of cum at the mirror over and over again. You, however...