Use that thing!

You tell Kako, "Use that thing!" She grips both of your buttocks, and wiggles them, never breaking eye contact.
"You are ready to be fucked?" She looks up at you adoringly, and stands up behind you. She lifts up her balls and rests them on your ass, which you stick out farther to make sure they don't fall off. They form a nice shelf, since Kako's cock is displacing your ass cheeks and pushing them out and up. You turn slightly to look at the mirror behind you, so you can see what you look like. What you see makes you crazy with lust.
You see your cheeks parted by a massive cock at least as big around as three forearms. Two cantelope sized testicles rest where your ass sticks out from your lower back. Your girl's cock trails down like a firehose, and then back up to her crotch. Kako notices you looking in the mirror and helps you strike a better pose so that you stand up straighter and push your ass out more. She then strikes a pose that accentuates her extra large ass and extra wide flaring womanly hips. She brings a nipple to her mouth and sucks seductively. Then she turns a bit and offers a good sight of her cleavage, pressing her far breast together with her hand. She uses her other hand to push up her close buttock so it looks twice as big at the angle she is at. She smiles with her nipple in her mouth at the sight, and her cock twitches every few seconds, indicating the sight turns her on as much as you.
You give a last look at the kinky pose. You are ready. While still looking in the mirror, you pull her hips forward, slamming her hard into your ass. It doesn't penetrate because she needs to guide it with her hand, but she gets the message. She pulls up her other breast and feeds the other nipple into her mouth, then grips some of her cock. Bracing her hands on her pelvis, she begins rocking. You feel her cock moving in your ass a bit with almost no friction, since the gallon of cum in you lubricates you and her.
You begin beating your meat as you watch the mirror. After about 10 minutes, you feel like you are going to cum. Kako nods, and you catch your load in a hand. As you cum, Kako grabs a larger amount of cock and puts her weight into it. You watch as six inches slide into you, and you feel yourself stretch wide. You don't feel pain through your cum, and the stretching feeling makes you cum harder and longer. She fucks another two inches inside as you watch. You must have taken another forearm's width into you! You beam as you see you are almost to the thickest part of Kako's cock. She starts rocking again, barely fucking you as you stop cumming. The stretched feeling is still there, and some pain surfaces as you come down from your orgasm. You look down at the cum in your hand, and notice a bulge in your front again. This time it is her cock, and you reach around and lube her cock a bit with your own cum as she pulls out, and it goes inside you with the next stroke, lubing your ass with your own cum.
You take one of Kako's hands and put it on the bulge in your front, which rises and falls with her rythem. She knows immediately what it is, and you see only her eyes smile because her mouth is covered by titflesh. "Keep your hand there, and feel this." You reach around to massage her balls resting on your ass, and she knows what you want. She cums immediately, bucking against your ass briefly, before wrapping her arms tightly around you and squashing your ass outward, her balls nestled on top of them pulsing deliciously. As you feel her cum, you put your hand over where her head creates the bulge in your front. She feels it too. She moans loudly, her nipples falling from her mouth. She immediately picks them up and wraps them under your arms and inserts the nipples into your mouth and then puts one hand on the pulsing bulge and another rubs your dick. "Chew on them a bit...make me cum harder..."
You cum into her hand immediately as you chew lightly on her nipples. "Fist your ass with it," you say, and she does quickly. You watch as your midsection swells again with her deposit. She keeps coming as you rub her balls and bite on her nips, a full minute longer. If you were a girl, you would swear you were at least six months pregnant! After she stops, she rubs your bulge of her combined cum and large penis. The pain in your asshole has stopped, you are used to the feeling of being essentially double-fisted.