"Oh, did I say you'd get a big butt?" Ben said, moving in front of Blake, his huge butt wobbling in front of Blake's face. "I meant to say I would." Ben suddenly leaned back, sending Blake's face right between his cheeks. Blake was suddenly very close to the butthole he was just recently fucking, and as great as that usually was, his fight or flight was telling him to struggle against whatever was about to happen.
Blake thought that Ben would let up some pressure, but he didn't, only pushing Blake's head harder against his butthole. Eventually, Blake could face his anus stretching open, until it engulfed his face completely. Not long after that, it slipped further down, engulfing his head completely, with Ben's butthole settling softly around his neck.
Ben didn't waste any time overly enjoying Blake's struggles, instead he put more pressure down on Blake's body, truly stretching his ass to it's limits. With a sudden stretching sensation, his butthole widened just enough to create Blake's shoulders, which sent Ben's ass gliding down Blake's body because of the pressure until he landed on the couch with a thud his butt settling around Blake's waist.
The motion sent Ben into ecstacy, immediately making him release a second time. Apparently Blake was somewhat enjoying himself as well, having came into the couch between their legs. Ben smirked, now knowing there was no way out for Blake. He only had to clench his ass before his anus creeped over Blake's butt, leaving only his legs to kick for freedom they wouldn't get.
Ben decided to get up from the couch, and savor these last moments. He looked back at his ass and marveled. Blake was only halfway swallowed by his butt, but it had already expanded by three inches. He could only imagine how big it would be after Blake was fully processed. With that, he started to clench rhythmically, steady sucking in Blake's legs until his feet were slurped up by her massive rear.
He was immensely aroused by Blake's futile struggles, which occasionally created bumps on his perfect round ass. He couldn't help but stroke his dick, which almost immediately made him cum again. After all that, he decided to take a nap, and fall asleep happy to Blake's futile struggles...
---
"Hey, Ben! Watch how you throw that thing around!" Henry said, leaning back as Ben shimmied into the bus seat. "Those yoga balls are about to escape their fabric prison!" This comment was completely correct. Ben's now-yogaball-sized butt cheeks were straining against his stretchiest pair of sweatpants.
"Oh? Then maybe we should free them a bit," Ben then pulled his pants down, revealing his ass in all it's glory, before promptly taking a seat on top of Henry. His cheeks easily engulfed the poor boy, and Ben could faintly hear him yelling 'get off.' After a minute or two he rose up, and Henry took a long, slow breathe.
"Geez man, y'know if I had an ass like that, I'd love to torture some of the sixth graders," Henry remarked. Ben's ear perked up at this.
"Would you like to see how my ass got this big?" Ben asked slyly.