Not a chance; you need that ass

Just as you reach the top of the stairs, your will breaks. Advancing on your mother, you grab her ass with both hands, groping it roughly.

"Ah! M-Marcus..."

Without a word, you push her down towards the floor. In order to avoid tumbling down the stairs, she has **** but to let you guide her down. Keeping her balance soon becomes even harder as you give her a shove forward. After a short tumble she sprawls ass-up on the edge of the stairs, her arms braced on the second-to-top step.

"Careful," she yelps, trying and failing to rise from the awkward position as you straddle her. "What are you--You can't--"

"Relax, Mom. Time for more medicine," you growl, yanking aside the tiny skirt of her outfit and pulling her ass cheeks apart. "I'm pretty tapped out, though, so we're gonna have to step up the tightness a 'lil bit."

"What do you--Oh. No, wait! I thought my... My, um, back door is supposed to be for emergencies! We agreed!"

"This is an emergency," you reply, spitting on your hand and rubbing it around your cockhead. "You haven't swallowed nearly enough jizz today."

"B-but I thought you and Cassidy were med... Medicalling..."

"Medicating?" Your voice is surprisingly calm as you continue lubing up your shaft.

"Yeah! You were medicating me lots last night, weren't you?"

Oh shit, that's right, you think. I lied about cumming in her mouth while she slept, didn't I? Woops.

"Uh, yeah, but that was before midnight," you begin, pausing to spit on her exposed asshole; she gasps and squirms as you continue. "...So, y'know, it doesn't count."

"What? Why?"

"I told you: you haven't swallowed enough jizz today."

"I'm... Pretty sure that's not how it works," your mother mumbles, but you can see the doubt in her eyes as she looks back over her shoulder.

"Of course it is, dummy," you sigh. "Look, I know it's hard for you to understand these things, but that's exactly why I need to fuck your ass ASAP. Can we stop with the questions and start with the anal?"

"And you're gonna cum in my--Um, you're gonna medicate me properly this time, right?"

"Uh... Yeah, of course. Duh." With that you push the tip of your member against her asshole, driving your hips forward to push past the initial resistance. Even after all the spit you applied, it's a very tight fit: you have to apply plenty of brute **** to work your way inside.

"F-fuu... Fuck, fuck, fuuuck!" Mom's cries get louder with every thrust, until she stops, bites her lip, and slams a fist against the stairs. "S-sorry for the language," she whimpers. "It's just... Tight."

"You fuckin' bet it is," you grunt, before slapping her jiggling butt a few times. She doesn't say a word, closing her eyes and breathing heavily as her son spanks her.

Must be more focused on the whole 'not swearing' thing... That and trying not to fall head-first down the stairs. Man, I'm really being hard on her today!

"Yuh... Y'know, Mom, I heard that your medication can be absorbed through the, uh... Bowels, or whatever."

"...Wuh..." She opens her eyes a crack. "W-what was that, baby?"

"My cum. It works just as good if I shoot it in your ass... Better, even."

"Really? Where did you hear--Aaah!" She's interrupted as you slam into her harder than before, finally driving yourself balls-deep while she pants and struggles.

"Yep, apparently it's the latest thing right now. Don't tell Dad, though... It's still experimental, and you know how he gets. Always the old-fashioned way with him, y'know?"

"Marcus, I'm not sure if--If--"

"Oooh, God... Too late," you groan, grabbing Mom's thick ass with both hands and burying your shaft inside of her. That thrust pushes you over the edge, and you begin pumping thick spurts into her warm, tight depths.

"Are you...? Oh..."

"Yeah, Mom... Take my fuckin' load, you stupid cumdump..."

Surprisingly, your mother notices the insult this time. "W-wait, what? What did you just say to me, young man?"

"Ungh... Uh..." You pause for a moment, tensing up as you shoot one last rope of jizz. "Well... It's true, isn't it? Your condition makes you stupid, and me and Cassidy are supposed to dump all our cum into you, so..."

"But you just can't say that kind of thing to your mother! It's totally ina-inapropit... And, uh... Rude!"

"How can it be inappropriate if it's true? That doesn't make any sense, Mom," you say soothingly as you pull your softening, cum-slick member out of her asshole. "You always taught me to tell the truth."

She looks completely baffled, still lying with her well-used ass in the air even as you stand up and stretch. "I... I don't..."

"You're a good mom, and you taught me well," you continue, offering your hand.

"Aw... Thanks," she replies, the confusion slowly fading from her face as she lets you help her up; it seems like your chivalrous act is doing the job nicely. "Can we go downstairs now?"

"Lead the way."

She straightens her "clothing" out and heads off, and giving you another eyeful of her jiggling rear end. With every swish of the far-too-thin skirt, you can see a trickle of your cum making its way down the inside of her thigh.