Story: Friendly Hentai Tome

"So pay attention, very closely," Nabiki Tendo said, going into full on sexy teacher mode. It suited her well. After a moment of thinking about it, that came down to personality and... probably the legs. God she had a great pair of legs. "The Chain Rule is used when you need a derivative of a function applied to another function. Hrm, how to explain that in a way that'll keep your attention...?"

She rolled off the seat, a sly look on her face, and turned her attention to a whiteboard that was being propped up at the side of the room. Then, unnecessarily, she bent over. "Let's say you wanted to find the rate of change for the curves on my body," she said, emphasising her point by sliding her hands down her feminine figure with one hand, while the other grabbed a marker, stuck the cap between her teeth and tugged it off, then spat it to the floor. "That's not a simple function. It's probably something like cos(sin(x)). The Chain Rule lets us differentiate that sort of function easily."

"Um, that wouldn't look like a woman's figure," Hinako interrupted, but Nabiki simply shrugged.

"It's just for demonstrative purposes," Nabiki shrugged. "So. The idea is, you split the two functions apart. You call the 'inner function' g(x), which in this case is sin(x), and the 'outer function' is f(x), which in this case is cos(g(x)). We can go over the proof of this later on if you really want, but the idea is that when you take a function of a function, your derivative will look like this -"

Then Nabiki wrote on the whiteboard, still bent over, shimmying her butt around. She knew what she was doing. She knew exactly how tasty her peach shaped kiester was, and had little trouble in flaunting it to keep a man distracted. That's why she wore those snug shorts all the time, or those jeans, hse knew how well they flattered her figure and could easily captivate a man's full attention - 

And then, on that whiteboard was written some nonsense: dy/dx = f'(g(x)) * g'(x)

"The simple version is; You differentiate the outer and inner functions separately, then multiply them together to get the full result," Nabiki said. Then dusted her hands as if she'd explained everything. "Got it?"

"Got it..." Hiroshi muttered to himself. Aha, okay. So if you were to try to differentiate x^x, then you'd have to treat them as two different functions and multiply together the result. Okay. So... g(x) = x, and f(x) = g(x)^x. Or was it the other way around? Should f(x) = x^g(x)? Ah, maybe they both gave the same result, or - 

Or... was he getting distracted again from what he should be focusing on? Nabiki's body, slender, mature. Dominant, mighty. With a mind behind it like a cold steel trap. Maybe he should try applying the chain rule to seducing her, instead?

Think of it this way: The inner function was them attempting to control Nabiki using the friendly hentai tome. The outer function then, is Nabiki's response to the friendly hentai tome, and her flipping it around to ensure she still has control despite becoming their 'friend'. She's clearly seducing him here, but she's also maintaining the pace at her own leisure. Teasing him, manipulating and guiding him instead of the other way around.

Okay. So what does it mean to take the derivative of 'using the hentai tome' in this metaphor? Well, a derivative is the 'rate of change', and in this case the things being changed are arousal and control.

Of course! Put like that, the answer becomes obvious! The level of control is y, the output of the function, and the level of friendly arousal is x! Alright then! Let's say the formula is something like y = 2x^2. You wouldn't need the chain rule to solve that, of course, but it helps demonstrate how it works, and besides which it feels roughly representative of how easily Nabiki's turning things against them. The inner function is 2x, the outer function is g^2. The inner's derivative is 2, and the outer's is 2g, so if you apply the chain rule you wind up with 2(2x), which becomes 4x, which is the correct answer.

"You know, you look really pretty today," Hiroshi said. Confidently, just outright said it. "Have you ever thought about going into teaching? I think you'd be very good at it."

"Eh?" Nabiki grunted in mild confusion while the other girls in the room simply titered. "W-well, I don't know about -"

"No, no, it's true! You've really captured my attention and made this topic more interesting than I thought," Hiroshi continued. "By the way, what kind of guy do you like? I've been wondering that for a while now, and so... You know?"

This was it. The application of the chain rule. By applying the function to a function and finding its rate of change, he'd worked out how to get around Nabiki's formula for control. Hit her with two different complimentary topics at once. Compliment her intelligence. Compliment her beauty. Keep that input inconsistent enough, and her formula would break, unable to handle both at once, until -

He had her sitting in his lap making out with him within a couple of minutes. The correct answers to various problems written on the board behind her in his handwriting. Each time, he'd complimented her teaching ability and her good looks in the same breath, goaded her into raising the stakes over and over again, and here they were, with his good buddy Daisuke not too far away necking with Miss Hinako. Perfect. Absolutely. 

"Mmmm~" Miss Hinako moaned. "Ooohhh, Nabiki, your plan worked perfectly!"

Huh? Plan? What plan?

"Mmm, yeah," Nabiki moaned. "I'm so glad my good buddies Yuka and Sayuri told me allll about that magic book you guys have. Made it so much easier to teach you about calculus."

Huh? Huh?! You mean, the two of them got played and wound up getting what they wanted anyway?! Nabiki pushed Hiroshi to the floor, straddled his waist, then tossed her top aside while staring down at him with a hungry look in her eyes. Absolutely ravenous!

"So, Hiroshi babe," she licked her lips. "Why don'tcha let your good buddy Nabiki take a look at that book. I'll be sure to make it worth your while."

=====

Ukyo was so fucking cute it wasn't even fair. Sometimes it felt like, if Ranma had maybe run into her before showing up at the Tendos, the two of them might be married already. Or! Or, they might have fallen back into an awkward kinda friend zone. Which was the opposite of the typical friend zone situation, where the hot guy thinks the cute girl is merely a close friend while the girl wants to bang his brains out.

In this case, though? Akane had developed a bit of a crush on Ukyo today. Seeing her so hard at work, expertly making those okonomiyaki perfectly to order, leaving every customer satisfied... She was almost as cute as Ranma in this maid uniform here, which she'd put on to help draw in more customers.

Mercifully, at last, the final customer of the day left, and it was just the three of them. Ukyo and Ranma began to clean up, but no no, Akane could not wait. Not one minute longer.

"Hey, why don't we... help take the edge off upstairs a little?" Akane asked. "This mess can wait about half an hour, right?"

"I don't know," Ukyo said. "If you leave something like this, you'll never get to it..."

"Yeah, and it'll be harder to clean later on," Ranma added. "Best to get it done now."

Akane twitched her nose and watched while the boy that was really a girl set about scrubbing surfaces, while the girl that was really a boy set about washing. In all honesty, Akane wasn't very good at housework. That hadn't changed at all. Cooking? A little improvement. Cleaning? She didn't know her own strength.

Still, watching the two of them get on like this was very much working for her. She racked her brains for what to do next. Have to get them upstairs! A yuri threesome sounded like it would really, really hit the spot right now. Especially after she'd been working so, so hard to make the three of them into such close sex friends!

Then, she had an idea. She crept up behind Ukyo, and grabbed her shoulders. Giving them a nice big rub down that made the okonomiyaki chef purr like a kitten.

"Don't mind me," Akane whispered in Ukyo's ear right before kissing her neck. "I'm just doing a friend a great big favour."

"You mean a sex-friend, right?" Ukyo asked, writhing a bit under Akane's touch. "The three of us are all sex friends."

"That's right, we are," Akane whispered. "Look at Ranma. Isn't she the hottest fucking thing you've ever seen in your life?"

Ukyo turned her head to look. A blush took control over her face. Akane brought her hands lower than Ukyo's shoulders. Down her spine. Around her waist. Ukyo kept on scrubbing away.

"I bet she'd do you a favour if you asked," Akane whispered. She began to circle her thumb around the waistband of Ukyo's trousers. Hooking them, and the underwear beneath. Huh? Boxers? Really? Well... she probably didn't have much girly underwear did she? No matter. She peeled those trousers down. The boxers too, and Ukyo dutifully, perhaps instinctively, stepped out of them. "You've been working so hard for so long, getting your bell run is just what you need."

"Yeah... I bet it is..." Ukyo muttered to herself. Now standing there with her bottom half bare, stealing occasional glances over at Ranma. Yes, that's right. Join his harem

Speaking of which, Akane strolled over to Ranma, took some cold greasy water in a pan, and then splashed the back of Ranma's uniform with it.

"Oy! Watch what you're doing!" Ranma yelped. "That's cold!"

"Oops!" Akane gasped. "Better take it off then, I'll get it washed properly." That much, she could manage at least. "Consider it a favour. A favour from a sex friend."

"Fine, fine," Ranma grumbled, and shimmied out of her maid uniform. Goddamn. Every time, Akane somehow forgot how stupidly hot and sexy Ranma's curvy body was. Seeing it like this was a rare enough event for her, but one she intended to make happen more often in the near future.

Akane pulled up a basin, filled it with hot soapy water and began to scrub the grease off, while her eyes were fixed to Ranma's hot body. Look at them both. Ukyo was slender, with a pleasant rump and long luscious legs, while Ranma was cute, curvy and short. There was such a strong contrast here.

"By the way, doesn't Ukyo look especially pent up tonight?" Akane whispered. Ranma turned to look, right as Ukyo was blatantly leering at Ranma. Brainwashed by booty. Hehehe! Can't really blame her. It was all Akane could manage to not lick that butt, or at least cop a feel. "I think we need to go in deep tonight. Make sure we leave her well and truly satisfied."

"Yeah,  I guess we'd better," Ranma nodded. "You're a good friend, Akane! Looking out for our needs like that. You might be an uncute tomboy with a violent streak a mile wide, but you got that going for you, for sure!"

"A good friend...?" Akane muttered to herself, a faint smile playing on her lips. "No. But I am a good sex friend."