"Since you are so keen on keeping a close eye on me, I know just the place to put you," Thea said with a smirk. 
Before Oliver could ask where that place was, he was yanked down from his place at her face. Things flashed by in a blur, but when he came to a stop, he was staring at his younger sister's leggings clad ass. 
"You seem intent on being a pain in my ass Oliver. I guess is just a big brother thing. But since I'm such a good little sister and I've missed you these last few years, I'm gonna give you a hand." Thea continued, slurring her words in her drunken state while her free hand pawed at her ass. Only when her thumb successfully hooked under the waistband of her leggings and panties and pulled them back, revealing her pale white ass cheeks. 
"Thea no! You can't do this! Bring me to Felicity!" Oliver screamed, horrified of the abyss of his younger sister's ass crack that he was staring into. 
"No way Oliver. We're keeping this little problem in the family, which means keeping you between my butt cheeks." Thea said, releasing her grip on her brother's body as the last word passed through her lips and sent the tiny archer tumbling down into her awaiting crack.
Oliver put out his arms to brace himself and stop his descent, but there was nothing to hold onto except the never-ending butt flesh of his drunken sister. Her smooth cheeks had no handholds to speak of, but the friction against them as he descended finally brought him to a stop halfway down her crack, suspended by his arms and legs braced against her buttocks. He looked up to address her, but just got a quick glimpse of her smiling face looking over her shoulder before she released her grip on her pants. 
With her tiny brother secured, Thea was ready to get back to some fun. She quickly downed another shot, having long ago lost count of how much she had had to drink. With a smile on her face, she strutted out towards the dance floor, giving her tiny brother his first glimpse of what it would be like to endure her hips on the move.
Nothing Oliver encountered on Lian Yu prepared him for the relentless onslaught of Thea's ass cheeks. The rolling of her hips with every one of her steps kept her cheeks on the move, rising and falling with every one of her steps. When her right cheek rose, her left cheek would fall accordingly, pulling Oliver in two different directions at the same time. He felt like he was going to get pulled apart with each step as the powerful friction between her soft flesh and his own shrunken body and clothes caused him to be tugged and stretched. He frantically tried to squirm and kick against her cheeks, trying to escape their hold on him, but the fleshy mounds had him right where they wanted him, and they had no intention of letting him go. 
By the time Thea got to the dance floor, she decided Ollie was ready for the main event. In her inebriated state, it didn't even occur to her to worry about her brother's safety. After all, he was a grown man, and she was just a teenage girl. He should be able to stand up to her soft, sexy ass all day long. Or at least, all night long.
She strode onto the dance floor and immediately found the group of friends she was with. 
"Thea! You're back!" Oliver heard the drunken girls yell. 
"Yeah sorry, my brother was just up my ass about me being here." They said with a smirk, clenching her cheeks around Oliver to emphasize her little joke. Needless to say, Oliver wasn't amused. Not that he could have laughed anyway, considering every clench of her cheeks squeezed all the air out of him like a deflating balloon. 
"Whatever girl, let's dance!" Another friend replied, just as the next song began to play. The girls immediately got back to dancing, and Thea didn't waste any time joining them. 
Oliver had gotten somewhat used to the rolling of Thea's hips as she walked, but her dancing was an entirely new situation. Rather than rubbing up and down on either side of him, Thea's cheeks now jumped from side to side as the brunette shook her hips on the dance floor, and they brought him along for the ride. Oliver's two dance partners immediately began to fight over him, jumping into action. But rather than pulling him back and forth, the giant cheeks were tossing him to each other.  The giant butt cheeks took turns slamming into him, one pummeling him while the other waited to catch him in its fleshy embrace. Oliver felt like he was caught between a giant pair of Newton balls, slamming him endlessly but never slowing down. If anything, Thea was speeding up. As she found her groove on the dance floor and lost herself in the music, the movement of her hips became more erratic. Sometimes the pattern would break, and one of her cheeks would be unable to resist taking a second smack at him before the other got its turn again. This was always balanced out eventually by a particularly strong smack from whichever dance partner got shafted. 
No matter how much fun she was having, Thea never lost the feeling of her tiny brother squirming for freedom in her panties. She didn't regret putting him there for a second. Oliver had abandoned the family for 5 years, and now he thought he could come back and boss her around? He needed to be punished, and her ass cheeks seemed to be the perfect method. She figured once he had been punished appropriately, she would allow him to start begging for her forgiveness. She figured he'd need to do some serious ass-kissing to get back on her good side, and she did not mean the figurative kind. 
Suddenly, the DJ pushed a single button on his console that turned Oliver's already miserable situation truly hellish. He changed the song, causing a sudden bass drop. Thea reacted to this the only way a drunk 17 year old looking to torture a tiny man with her ass could: she began to twerk. 
The effect was instantaneous for Oliver. Thea's cheeks no longer had the patience to take turns with him. Her ass was now not moving back and forth, but in and out, her cheeks clapping around him over and over again as her ass rapidly moved back and forth. As she moved, Oliver was also dragged in and out of her crack, given brief periods to slide around as her cheeks spread between claps. Oliver tried to brace his limbs against her cheeks, desperate to steady himself. He managed to get a foothold, but this did little to stop the incessant clapping, compacting his entire body on every strike. At the same time though, Oliver knew this was his chance to escape. Her cheeks were spreading enough to give him a window, and she was lost in the music on the dance floor. He'd have to make a jump for the opening when her cheeks spread, then fight his way out of her panties. He counted down as he prepared to make his move, timing the claps of her cheeks, feeling the painful squeeze of everyone. 3.... 2.... 1...
What happens?
1. Thea feels Oliver's escape attempt and decides to keep him in check by forcing him up her asshole. 
2. Thea feels Oliver trying to escape, and punishes him by hip checking the wall, hard. This knocks Oliver unconscious, and he wakes up the next morning in a sleeping and hungover Thea's ass. 
3. Oliver escapes successfully, but falls out of his sister's underwear to the ground, landing hard on the dance floor. The impact breaks one of this legs, leaving him barely able to move at his giant sister's feet (probably death option)