When you awake in a spider's web, dangling from the sticky string with your entire body cocooned in silk, there is a certain expectation of what would happen next that immediately runs through your mind. Your expectations are soon proved false, though, as you see the owner of the web in question coming towards you. 

She is naturally very spider-like in appearance, with the 8 limbs one would expect from an arachnid, but she isn't quite the giant, monstrous thing you were expecting. Instead, she is extremely humanoid. Almost cute, in fact, as you notice when her purple-skinned, five-eyed face is inches away from yours. 

"I'm not going to eat you" she said with a smile, showing off a pair of fangs that did little to ease your suspicions. "In fact, I think you're going to be doing most of the eating" 

Before you could ask what she meant, she scuttled off for a demonstration, returning with what looked like a donut in one of her many hands. 

"Open wide" she said, her sweet tone of voice and the fact that you were essentially helpless compelling you to do what she said. 

She shoved the donut in, and you chew and swallow, finding it to be surprisingly delicious. 

"There's plenty more were that came from" she said. Before she leaves to find another donut to feed you with, you interrupt her, asking her why she's feeding you. 

"Oh, I almost forgot to tell you, ahuhuhu. I have very specific taste in men, and you were the only one lucky enough to wander into my web. I like my men nice and fat, so I'm going to keep feeding you spider donuts until you're big enough for me. Don't worry, I'll be sure to make it worth it for you while I fatten you up"

She notices a bit of hesitation in your expression. Despite the surprising friendliness of the spider, something still irks you about this scenario. 

Muffet sighed. "Fine, just give me a second" she said, scuttling away and coming back with an entire box of donuts. She put her many arms to use, using one to hold the box, and another to open it, while unraveling the cocoon with two more. She frees the lower half of your body, and you flex and shake your legs, delighted to finally be free, just as you realized that you're completely naked. 

Before you have time to feel any shame, a donut is crammed into your mouth, while Muffet displays her impressive multitasking skills again, wrapping one of her hands around your stiffening shaft, and pumping it delicately with a surprising amount of skill. 

"Keep chewing, and I keep stroking" she said, as you instinctively continue chomping on the donut. For a moment, everything feels so natural, and you chew and swallow without the need for a break, while Muffet's deft strokes motivate you to continue. You do everything you can to keep from cuming too soon, although Muffet's relatively slow rhythm made it much easier to prevent an early release.

She frees her hand from your cock, as the final donut of that box passes your lips. "Don't worry, there's more where that came from" she said, pausing before scuttling off, to look at the results of what she had done so far. She unravels more of the cocoon, now exposing your torso to the lustful spideress. All of those donuts did a number on your body, and you now sported a pudgy belly instead of a flat stomach. Any regret you may have had for all those years of dieting and working out going to waste were immediately put to the side, as Muffet nuzzles her face into your belly, stroking it with each of her many hands, covering as much of the tight, flabby skin as she could. Her belly rubs felt almost as good as her handjob, and the amount of her doing both at the same time made your head spin. You imagined that, if you continued eating as she asked, that was a pretty likely possibility. 

"You're looking pretty good so far" she said proudly. "But I need you to be huge before I can really be satisfied. And if I want you to be huge, I think we'll need to do this a little bit faster"

She summoned a legion of spiders, each carrying a donut, sometimes two, on its back. They marched in single-file towards you, before stopping right beside your mouth. 

"Open wide" Muffet says, fixing one hand around your cock, laying two on your belly. You open up, and the spiders march continues, with each dropping the donut on their back into your mouth, before heading back to the end of the line to pick up another donut, and presumably feed you again. It was like a conveyor belt, only with more spiders and handjobs. 

While you were occupied with chewing, as more and more donuts were pumped into your mouth by a legion of spiders, Muffet returned to stroking your cock, while, as you had predicted, rubbing your expanding stomach with the other hand. 

Your belly, at this point, had reached enormous sizes, as the spiders method of delivering donuts to your mouth was much more efficient than Muffet could ever manage on her own. Your stomach had now reached approximately the size of your own body, sagging down to your feet from gravity. 

Muffet blushed, licking her lips at the sight of your bigger belly. While still rubbing your belly and cock, Muffet allowed another of her many arms to venture down her panties, giving herself some relief as your stomach continued to grow. She leans in to plant a gentle kiss on your forehead, before returning to feverishly masturbating herself. 

The process continues for a while, with Muffet rubbing herself and you, and the spiders continuing to fill your mouth with what you are forced to assume is an infinite supply of donuts. Occasionally, you are given a break from being fed, so Muffet can slide her fingers into your mouth and give you a taste of her juices. You confess it tastes pretty good, but not quite as much as her donuts. 

As you gulp down your thousandth or so donut, you begin to notice your body undergoing more changes. Your belly isn't round anymore, and has swollen into a wobbling blob shape with countless rolls of fat. Your arms and thighs have thickened to the point where they're difficult to move, and you seem to have a few more chins than when you started. Your ass has become gargantuan too, and your cock is buried somewhere deep between your corpulent thighs, but that doesn't stop Muffet from tugging it still. The army of spiders carrying food to you now stops, scattering in every direction. You hear a creaking sound, and you see the web you were one trapped in strain underneath your weight. Muffet herself even departed, but promised she would return in just a moment. 

The web finally tears, with bits of silk still clinging to your ass. It is that very ass that cushions your fall, as you barely feel anything as you plummet onto the hard stone ground. The floor shakes beneath you, and your entire fatty body wobbles from the impact, with your belly and man-boobs especially jiggling comically all around. 

"Sorry about that, I didn't expect you to get this big. I guess I got a little carried away"

You attempt to nod, but your many chins make it difficult to move your head. 

Muffet gazes upon your fully-fattened form, finally satisfied with your figure and drooling slightly. She plunges herself between your thighs, no longer merely tugging at your cock, but taking it into her eager mouth. Fortunately, she seems to know what she's doing, and the pair of fangs you remember her having don't seem to get in the way. Instead, she brings you to completion with expert sucking, swallowing your resulting load with the same eagerness you ate all those donuts. 

Soon after, Muffet finally satisfied herself, rubbing once again to your gloriously fat body that was apparently turning her on beyond words, soaking the front of her pantaloons in her spidery sex juices. 

Without a word, Muffet climbs onto your body, curling up and resting on your mountainous belly. You get a better view of the cave from your current position, and you can see that your body takes up most of it, with just the slight bit of room left to allow passage through the entrances on either side. You watch Muffet fall peacefully to sleep, as you let out a belch and slip into a food coma of your own.