"...Ass!" Mark said.

Nikki blushed slightly at him. She must have known that Mark had been an ass man, he'd been checking out her sweet booty all the time lately. The way her tight shorts clung to it during volleyball was enough to drive him wild. He was lucky to have friend who was this hot and willing to let him do this, just so she could use his invention.

"Okay, but could you turn around for a few seconds? It's embarrassing having you watch me strip."

Mark's eye bulged "Wait, you're letting me touch it NAKED?!"

"Well yeah, isn't that what you wanted?"

"Y-Yeah!" Mark stammered back.

"Okay then turn around and close your eyes while I get ready."

He did as Nikki instructed. He could hear the sounds of her taking her clothes off. His heart beat fast, he was so excited! He was about to grope his classmate's sexy ass! Today was easily the best day ever. He had made a breakthrough in modern science and was gonna get a hot slice of Nikki's booty pie. Suddenly he heard a weird noise.

Opening his eyes he saw a human sized portal directly in front of him. He spun around to see Nikki buck naked and holding the device. As soon as he turned she began pushing him in the portal with her bare foot.

"Nikki! What the hell?!" he shouted.

"There's no way I'm gonna pass this up." she grinned as she put more weight on her foot, pushing Mark further in the portal "You'll get to be my shrunken little play toy for a while AND we'll be testing out the device. That's what you wanted right? Don't worry, you're still gonna get to touch my ass. Only, it'll be a lot... bigger."

Mark was scrambling, trying to get a grip on her carpeted floor to stop himself from falling into the portal. He should have seen this betrayal coming. Nikki loved using him as a toy to amuse herself. Of course she would try to shrink him.

Her sexy leg was strong from years of volleyball, he didn't have much of a chance against her kicking. Mark managed to catch a short glimpse of her pussy before she kicked her foot again, this time right on his face. He could smell her gross foot stench on his nose before she kicked it off him. He fell backwards into the portal, the smaller exit of which was right above the palm of her hand.

As Mark fell a short thought passed through his mind. "Well, she said I could still touch her ass. It can't be that bad right?"

Mark landed with a dull thud on the palm of Nikki's hand. Everything seemed gigantic to him, but really he was a much much smaller size. Somehow his clothes were gone too! Did she do that?

"Nikki!" he called out to her. "Where are my clothes?!"

"OKAY MARK LOOKS LIKE YOU MADE IT THROUGH THE PORTAL JUST FINE." she said in a booming voice.

Great. She couldn't hear him. He was so small that his tiny voice couldn't make more than a whisper. How small did Nikki shrink him exactly?

Before he had time to think Nikki began to move, he could feel his gut churn from being accelerated at such a dizzying speed. She crawled on her bed, stuck her nude ass up in the air, and put her head down on her pillows. In this position her butt cheeks parted naturally and she dropped him right on the line of her crack.

"I guess you really enjoyed all those times I sat on your lap with my big sexy butt, huh?" he could hear her taunting from what seemed like miles away. "Well now you're going to get all the booty you can handle, hope it's not too dirty for you."

Mark landed on her skin but this landing was a bit softer than last time. Her two ass cheeks rose above him into the sky like two high walls, insurmountable. On one side her butt crack's skin got bumpier, leading to her taint and eventually her pussy. On the other side it was smooth but leading to a giant pit. Mark felt a heaviness in the bottom of his stomach as he thought of what it could be.

Taking a short walk forward he saw it: her asshole. It was like a massive sinkhole was shaped into the earth, but made of fleshy ridges of brown skin, all meeting at a singular point. It reminded him of the sarlacc pit from Star Wars, and he shuddered to think of it swallowing him whole. There was a dull warmth emanating from it, and he could smell her pungent earthy scent lingering in the air.

Just then Mark realized how small he was. Just one of her anal wrinkles was bigger than him. It looked like her asshole could swallow multiple buildings compared to his new size. He was like a grain a sand, a spec of dust, not even tall enough to climb a penny lying flat. The monumental anus would rise and fall slightly, in pace with Nikki's breathing.

"NIKKI!!" Mark screamed. "YOU MADE ME TOO SMALL!"

Nikki couldn't hear his voice, it was too quiet and too far away. She hadn't checked his size before dropping him on her ass either, she just assumed he came out the portal an inch or two tall. It wasn't even one out of her three minutes that she was keeping him down there and she was already bored. What does she do?