Huge

"I want the biggest dildo you've got." Said Samus.

"No you don't." The AI said. "You would never get even the tip in, I suggest starting smaller. I think I know just the size for you."

Samus was disappointed, but also excited, just how big was the largest dildo they had? "Fine, I'll take your stupid 'smaller' option." She huffed.

"Very good." Said the AI. With that a floor panel slid open, and out emerged a monstrous, pink, plastic cock, easily wider than both of her shoulders and longer than she was tall! "This prototype dildo is perfect for someone of your 'capabilities', measuring in at 14 feet long (not including the base,) and 5 feet wide."

Samus gulped heavily, her knees wobbled, her butthole clenched, and her soft girlcock instantly belched out a huge globule of cum. So big was the volume of her involuntary ejaculation, that it **** her urethra to dilate open nearly an inch wide, stinging her cumtube as it did so.

"Umm, I m-might need a little h-help t-taking all of that." Samus said, her voice trembling.

"Certainly, Miss Aran." Replied the AI. "First I will inject your anus with a relaxant, which should help you on your way down."

"Way down?" Puzzled, Samus looked around, realizing with alarm that she was now perched on top of the monolithic dildo. "Wait, how did I get here, whaAAAAA-"

She cut off as the AI used some robotic tentacles to quickly wrench open her fat butthole, gripping and digging into the puffy rim of her swollen anus with industrial strength. Her screams of terror turned to screams of pleasure as the AI injected her straining ring of flesh with a nearly lethal dose of swelling agents, aphrodisiacs, and muscle relaxant, sending her sensitivity skyrocketing!

"OH MY GOD YESSS, MY ASSHOLE FEELS SO FUCKING GOOOD!" She bellowed, as the tentacles pulled her hole open a foot in diameter. "STRETCH IT WIDER, HARDER, BIGGER! I NEED IT! FUCK MY WORTHLESS HOLE WITH THAT GIANT COCK!"

The AI complied, dragging her down by the anus, but her hole wouldn't fit around the giant toy, given that it was still 4 times wider than her gaping backdoor. So the machines set to work, yanking her ruined sphincter open even wider, and wider, completely destroying it for anything but body-sized insertions. Only objects like the one below her would ever be large enough for her to feel a thing.

"Fuck yesss! Stretch me, wreck me, permanently OBLITERATE my hole! I never wanna even SEE a normal cock again!" Her own respectable 8 inch long cock, apparently hearing this, became permanently flaccid, but was still gushing a steady stream of cum down her shaking thighs, it's own hole gaping open 2 inches wide out of sheer submission.

The tentacles kept pulling on her trembling asshole, slowly stretching it to 2 feet wide, wide enough to fit both of her legs, thick thighs and butt included!

The AI finished, having pulled her rear end open 3 feet wide, and initiated the second stage of it's plan. Two more mechanical tendrils came down and grabbed her ankles, wrapping up around her legs, digging into her fat, jiggly thighs, before pulling her legs open into a split.

Her incredibly stretched and sensitive anus kept overloading her senses with shock after shock of orgasmic pleasure, so she wasn't exactly focused on her legs, but now she looked down, and saw the arms place her on the tip of the monster, her gaping butthole wrapping around a third of the dildo's head. This sent her over the edge, the feeling of the rock-solid polymer grinding into her fat rim causing her cock to squirt even more, shrinking and gaping open further, as if in jealousy of her mighty fuckhole, wishing it could take half the things her butt now could.

"Please, I can't wait any longer, I NEED this in my ass." Samus pleaded, her eyes watering, her nose (and limp, gaping dick) dripping a steady stream of viscous slime. "I just wanna be a gaping hole for hyper-sized dicks, a good little onahole, happy to take as many cocks up my ass as possible. And my dick, I'm never gonna fuck someone with it, so I might as well use it for my intended purpose in life, satisfying monster cocks!"

The AI, hearing all this, was mildly taken back, so it asked her one question before completely, and utterly pulverizing her insides; "Are you sure?"