He gets a logical blowjob

Adam leered at his older sister’s breasts. “I’d much rather stay here with you, Kathy.”

Katherine narrowed her pretty blue eyes at her brother and cupped her breasts.

Adam smirked. The sight of his busty older sister instinctively trying to give him a better look at her breasts while she was trying to act like an authority figure was absolutely intoxicating to him.

“Mom wants you,” she said. “You should go down and help her.”

Adam reached out and pinched her right nipple.

“Ow!” Katherine clenched her fists. “I’m gonna ki-”

“Sorry!”

Katherine’s expression softened. “It’s okay.”

“I’m not gonna go down and help Mom right now,” Adam said. “Sorry about that.”

“That’s perfectly alright,” Katherine smiled. “Mom might not forgive you, but I will.”

“You’ll always forgive me, huh?” Adam said.

“Always, little bro,” Katherine’s expression turned serious. “But only if you show me some respect and apologize first. I’m not about to become your doormat.”

“Hm,” Adam replied. “Speaking of doormats, a doormat is a person who doesn’t stand up for herself, right?”

“Right,” Katherine replied.

“And you’re not a doormat.”

“Damn right I’m not,” Katherine said.

“So logically, you should give me a blowjob any time I call you a doormat.”

Katherine’s face went slack. Her soft lips opened again, showing Adam her hot wet tongue that he had been looking forward to enjoying for so long. He smirked and sat on the edge of his sister’s bed.

“Yeah... you’re absolutely right,” Katherine shook her head before she turned to glare at him. “But don’t think that means I’ll ever do anything else with you, you creep.”

“You sure about that?” Adam chuckled. “You are kind of a doormat.”

“Am not!” Katherine said as she got down on her knees in front of him, her tits wobbling as she reached towards Adam’s pants.

“Are too!” Adam taunted.

“Shut up, loser!” Katherine swiftly unbuckled Adam’s pants. Adam lifted his legs to allow Katherine to pull his pants down.

“Make me,” Adam watched as his well-endowed older sister grabbed the sides of his boxers and pulled them down, revealing his throbbing member.

“Hmpf,” Katherine glared up at him for a moment before she refocused her attention on his cock.

His sister’s warm breath wafted over his dick, causing it to twitch. Katherine moved closer and pressed her wet lips to his cockhead. Adam almost came at the sight of his older sister kissing the tip of his penis while her large breasts jiggled enticingly with her every movement.

Katherine gave the tip a gentle lick before she opened her mouth and engulfed the head of his cock.

“Ah,” Adam was in heaven as his hot older sister swirled her tongue around his cockhead as she slowly took more and more of his member into her mouth. Waves of pleasure shot through his body as Katherine began sucking him in earnest.

Adam delighted in the slurping sound his sister made as she took his cock out of her mouth and began kissing and worshiping the sides of his rock-hard member.

“Oh fuck,” Adam gasped as Katherine inhaled his cock again and began sucking him back and forth, taking his dick deeper into her mouth with every repetition until he was positioned at the very edge of her throat.

Adam reached his hands down to fondle his sister’s tits.

Katherine spat out his cock and glared up at him. “Hands off my breasts, pervert!”

“Sorry, Kathy,” Adam grinned. Having this level of power over his older sister was giving him a heady feeling.

“It’s alright, Adam,” Katherine smiled before she grabbed his cock and began sucking again.

“Sis, you’re sucking your younger brother’s cock,” Adam said, the incestuous nature of the act thrilling him immensely.

“Yessh ah uhhm,” Katherine didn’t even bother taking her lips off of his cock to reply. Her blue eyes watched him innocently, as if she found nothing innately perverse about what she was doing.

“A-ah! And you’re doing it because I called you a doormat,” Adam grunted as Katherine took his cock even deeper, making a lewd gagging sound.

“Mhmmm,” she hummed. The vibrations sent shocks of pleasure coursing through his member.

“So it must follow that you really, really love giving me blowjobs.”

Katherine stilled and stared blankly ahead with Adam’s cock still in her mouth.

What a beauty.

“Mmmmm!” Katherine suddenly resumed the blowjob with gusto, moaning and whimpering with pleasure as she took him into her throat. She reached a hand under the waistline of her pants and began moving it back and forth between her legs.

Holy shit, is Kathy masturbating?

The visual was too much for Adam to handle and he came down his sister's throat.

Katherine gagged and dislodged herself from his cock, but Adam wasn’t finished cumming and lines of thick semen fell onto her face and breasts.

“Ew!” Katherine coughed and spat white cum out of her mouth. “That’s fucking disgusting, how could you cum in my mouth?!"

Adam grinned, still incredibly turned on despite the fact that he just came.

“Sorry!”

“Ah, don’t worry about it, bro!” Katherine smiled widely as cum dribbled down her face and breasts.

“Wow, I really loved doing that, Adam,” Katherine said. She bent down and kissed the tip of his cock again. She looked up at him with pleading blue eyes. “Can I please give you another blowjob?”

Adam just smiled. Before he’d invented the logic device, so many of his deepest, darkest fantasies had been impossibly beyond his reach. Thanks to his nifty little invention, any fantasy of his could come true.