Nikki smiled to herself. She couldn't feel Mark's presence trapped inside her panties, but in her mind she knew he was down there. Sitting on a shrunken boy toy in class was pretty exciting, and thoughts started to fill her head of how she could tease her little friend. She could start by rubbing her ass into the hard seat, rolling her juicy butt cheeks over him. He was already so far up her crack that just by leaning back she could smother him with her sweaty asshole. Maybe she could even sneak a little fart on him...? Her brainstorming came to an abrupt end when the teacher called on her.

"Nikki!"

"Y-yes?!" she stammered, being brought back from her fantasies.

"You better not be looking at your phone over there again! Today's class is important! If you don't pay attention you're not going to pass the test next week!"

"Okay! jeez..." she replied, that last part under her breath.

Reluctantly Nikki opened up her textbook and followed along with the lesson. Seems like she wasn't going to any have fun teasing her tiny friend this period after all. She needed to concentrate on the lesson and ignore the little passenger in her panties. Oh well, Mark was so far up her massive butt crack that his 1-inch body wasn't going anywhere.

----

While Nikki was right about him not going anywhere, she was still wrong about one thing: Mark was not 1-inch tall. Due to her earlier mistake Mark was shrunken down to a near-microscopic size, about as big as a grain of sand.

"How could she not have noticed something is wrong by now?!" Mark thought to himself, frustrated. "She dropped me in her ass, farted on me, walked all the way to class, and sat down on me without even checking if I was the right size! Is she stupid or something? Does she not care?"

For the moment, no. She was too busy trying to copy down notes to even think about Mark's situation. If she didn't pass the upcoming test her grades would be in a dangerous spot. Not quite as dangerous as where her little friend was, pinned to the chair by her booty hole. Even something as small as her anus still dwarfed the boy in size. Its puffy wrinkles pressed into his body, wedging him snugly between them. He counted himself lucky she wasn't sweating right now. If a single droplet of sweat happened to roll down her ass crack it could drown him underneath her pink hole. For now he had no choice but to wait inside Nikki's cramped humid crevice, while she focused on the class up above.

Leaning forward into her notes, Nikki's butthole slowly raised upwards, off the chair. Mark finally felt freedom from her gross pucker, or at least he would have if it hadn't snagged him by the arm and lifted him upwards too. His arm was clamped inbetween the folds of her anus like it was in a vice, and the rest of him was partially stuck to her with the help of the sticky oils that lined her skin. It was so dank and slimy next to her asshole that he stuck to it like fly paper, trapped while his arm was crushed.

Nikki's asshole was motionless, giant and unfeeling towards Mark's struggles. It felt like it was so active before, but now it was completely still. He could scream and pound on it as hard as he could, it wouldn't even flinch. Not that he had a chance to fight back, when Nikki leaned forward in her seat something else began to happen.

Her panties, deftly hugging the curves of her butt, shifted slightly. As she moved her hips forward, Nikki's round posterior pulled on the fabric. Also, thanks to her playfully spreading her cheeks before sitting on Mark, the underwear rode all the way up her ass. It invaded the depths of her crack, just stopping dead in front of the dirty hole. Completely by chance, a small, insignificant piece of lint got pulled up with the girls panties, and was lightly touching her backdoor. Even as tiny as the piece of lint was, it was still the size of a house compared to Mark. His strongest punches couldn't do anything against the colossal asshole, but the lint was able to faintly tickle it. Mark felt rumbles give way as the anus began to stir.

"Oh fuck! It's tickling her!" Mark yelled in panic.

In reaction to the lint Nikki's asshole started to spring back to life. On reflex it began to contract to try and get rid of the tickling sensation. Puffy flesh engulfed Marks whole body, pulling him inwards with the other huge anal wrinkles. He was smothered on every side by sticky lumps of skin until the anus unclenched and expanded back outwards. Mark tried to pull himself free, but now both his arm and his leg on one side were trapped inside the anus. Still being itched by the piece of lint, the giant hole contracted again, sucking Mark further inside. He desperately struggled against the pulling force, hurriedly digging through mounds of sphincter meat in a race to stop himself from being sucked inside. As hard as he tried it was a race he was slowly losing.

Meanwhile Nikki was still absorbed in class, with no idea what was going on in her bottom. The small piece of lint itching her body didn't even register in her mind, her ass was acting completely on reflex. She was calmly scribbling notes on her paper while her friend was fighting a life or death battle with her big fat ass. It was going to devour him whole, slowly chew him up and swallow him, without its owner even realizing. She was just sitting there, having completely forgotten about Mark for the time being. He was about to be eaten alive and had no possible way to get her to hear his screams.

"Nikkiiiii!!!" he shouted. "Your asshole! Stop your asshole- I'm too small! It's swallowing meee-MMMPPHHUURRGH!!!"

The uncaring anus clenched again on Mark, still trying to get rid of that pesky itch. With every flex he was sinking more and more into her asshole until he was no longer visible to the outside world. Oily walls surrounded him on all sides, pulling him deeper into the darkness. It smelled awful in there, the flesh was stained with the stinky remnants of past meals. Mark tried to not gag at the stench, even though he knew it would only get worse as time went on. The lint wouldn't go away, it continued brushing across the pulsating folds of Nikki's anus, encouraging it to keep contracting.

Mark had just barely escaped the metaphorical jaws of Nikki's asshole from swallowing him before, but this time it looked like he was fucked. The slime, the thick mucus-like anal juices that had once helped him pull himself out of Nikki's anus were now having the opposite effect. Instead of being lubricated enough to pull himself out, now he was lubricated enough to help the asshole pull himself in. The girls heavy turd-cutter would squeeze down on his body and hot gushes of slime would slather him from head to toe. The deeper he went the more rancid it got, the smell was so intense it felt like it was physically burning him. Or it could be the blazing heat of Nikki's inner ass, either one. Worse yet, in trying to breathe Mark got some of the disgusting slime in his mouth and was forced to taste her shitty juices.

The sticky anal mouth continued its consumption Mark's helpless body, all without its owner knowing. Every clench was excruciating, but these were only light twitches in response to a tickle. If Nikki was clenching her asshole on purpose Mark's body would be popped like a grape. He was nothing, a mere speck compared to the glory of Nikki's gigantic ass. None of it mattered anymore. He would have given all of his possessions, even the modified portal device in exchange for her to blast him out with a fart right now. Anything to stop him from being sucked all the way inside her bowels.

But nothing happened. Mark felt his legs enter a spacious room, followed by the rest of his body as he slumped through the other end of Nikki's hole. The air was sweltering hot, like a sauna, and the smell was a hundred times worse than the outside. Mark fell to his knees and wretched on the surface of the fleshy bowels. Back on the outside the piece of lint finally loosened and fell down the giantesses panties. The massive shithole gave a few more pumps until it couldn't feel any more disturbances and then stopped moving altogether. It was too late for Mark now. He was already past the wrinkled gate and burning inside hell. He was trapped inside the ass of his unaware friend and she had no way of knowing he was in there.