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Casey hopped over the turnstiles of the turtles' lair and looked around hopefully. April wasn't picking up her phone, so Casey had to find someone else to bother. Unfortunately, the living room was empty, aside from a few roaches and slices of pizza that have been left on the floor so long they might have gained sentience. She wandered in the direction of the kitchen, hoping someone would be in there, but she heard noises coming from Donnie's lab. The sound of something getting knocked over, and an exasperated-sounding string of swears. Who better to annoy than Donnie?
She trotted excitedly to the lab door and threw it open, stepping inside and letting it slam behind her.
"Heyyy Don-" she started, freezing when she saw the scene in front of her.
Donnie was sitting in his swivel chair. Mikey was on his knees between his legs. Mouth-on-cock. Both staring at Casey like deer in headlights. The silence was deafening. Mikey broke the silence by pulling off his brother's cock with a soft wet 'pop'.
"I- Um- Casey look, I can explain-" Donnie stuttered, flustered. Casey shook her head at him and grinned mischievously.
"No, I knew. I knew you guys must've messed around like that. Going through puberty all alone down here with nobody but each other…" she bit her lip and shook her head again triumphantly, "I fucking knew it."
"Okay well," Mikey finally said, "Can you like, leave? So we can finish?" Donnie kicked him in the leg and glared down at him. Mikey smiled innocently back up at him.
"Uh, can I watch?" Casey asked bluntly. The two brothers looked at her wide-eyed again.
"Um, no. You can't. Why would you-" Donnie sputtered, "Why would you want to?"
"It's hot," Casey shrugged, "I like brother-on-brother stuff."
"Dude have you like, thought about this before? Like, thought about all of us banging?" Mikey asked, absentmindedly rubbing his hand over Donnie's inner thigh. Donnie stiffened and waited for Casey's response.
"Well, yeah I guess," Casey shifted her weight from foot to foot and looked around the room, suddenly avoiding looking at the turtles in front of her. Mikey looked up at Donnie before asking the next question.
"And you think it's hot?" Mikey asked.
"Yea, pretty much. So… can I watch now?" she responded, looking back at them again and grinning. Donnie sighed.
"You can sit on that counter," he gestured to a countertop beside where they were sitting, "Don't knock anything over." Casey happily hopped onto the counter and looked at them expectantly.
"Are you gonna like… y'know… touch yourself while you watch?" Mikey asked, voice shaking, presumably from excitement.
"Do you want me to?" she asked, already reaching a hand down to unbutton her jeans. Mikey looked up at Donnie for his approval. Donnie nodded.
"What would be the point of watching if you didn't get off to it?" Mikey grinned.
Casey pulled out her cock and ran her thumb over the tip excitedly. Mikey went to town resuming what Casey had interrupted. Donnie jolted and grabbed Mikey's head, throwing his other arm back to brace himself on his desk. Casey noted the beakers and other sciencey stuff on the floor beneath him. That must've been what Casey heard being knocked over.
She intently watched the scene in front of her. A scene that she'd been imagining for years. Well, maybe not this exact scene, but similar ones. Maybe Donnie exploring Mikey's body, helping his little brother understand his anatomy. Or maybe Raph and Leo going at it, trying to top each other, trying to assert their dominance as the stronger brother. Or maybe Raph convincing Mikey to do things to him in return for favors.
Her own ideas mixed with the very real image of Mikey with a mouthful of Donnie's cock and sent her rocketing to her climax. Her head pounded and she groaned as she came, brain filled with fantasies of her best friends touching each other.
As she regained coherent thought, she realized she wasn't the only one that had reached her peak. Mikey was sitting on the floor panting, cum dripping down his face and dripping onto the floor. A lot of cum. How much do turtles jizz?
Casey tucks herself back into her pants and crosses her legs, trying to seem nonchalant, as if she didn't just have the best orgasm of her life watching her friend blow his brother.
"So do… do all you guys do that stuff? With each other?" she asked, trying to stabilize her quavering voice.
"Yeah," Donnie responded, too exhausted to be embarrassed.
"So can I watch all of you?" she asked, smiling.
"If the others are okay with it then… yeah," Donnie responded, smiling back.
"Awesome," Casey leaned back on the counter and stared blankly at the ceiling, imagining all the stuff she might get to see. All the things she's ever fantasized about. All the things she HASN'T fantasized about. She was about to enter a whole new world of experiences.