This was a dusty old story written on a dare way back when, and in an effort to build up a back library of works I've given it a polish/editing.
It goes without saying that I do not own the characters used within (something which I'm sure we're all grateful for.)

Biology Lesson

Jack Darby x Arcee

A rusty, scrappy arm reached up and swung towards her chest. A whirr of abused joints echoed in the small chamber. The facial features stayed blank as it shuffled forwards.

Arcee ducked and swung, sweeping her leg against the back of the target's knee joints. A summersault forwards and she brought her foot crashing down on the fallen dummy. It was long days like this that made her glad the silo's architecture included space to train. Or as Bumblebee had dubbed it, space to vent. The reinforced cement was sturdy enough to survive anything short of a deliberate strike from Bulkhead's mace. Knowing she could swing the dummy against the wall like a toy was a satisfying comfort.

The entire day had been a write-off. The Decepticons had been caught mining for raw energon in the desert, but by the time they had mobilised, it was too late. The mine was empty, and the vehicons had already fled. Minus the small token force that had stayed behind to buy the rest some time. Cannon fodder was all the more annoying when using the ground bridge, and their weaponry both burned through their dwindling energon reserves. So much so that to help conserve energy, Arcee opted to drive back into Jasper instead of bridging to Jack's garage.

And when she swung by the burger restaurant to pick her partner up, she was forced to watch as the girl Sierra stood around chatting idly. There was nothing spectacular about the exchange, except for just how long they talked. Jack would square his shoulders back and speak slower in that calm, confident voice he had begun to use more often. Sierra, however, wasn't responding much, and after officially getting fed up with watching, Arcee switched on her Sadie hologram and interrupted them.

In hindsight, Arcee had to wonder what was more frustrating to poor Jack. That his conversation was interrupted by his living robotic motorcycle partner or that Sierra looked utterly unimpressed by the lithe and leather-clad Sadie. Either way, Arcee wasn't too worried about disrupting the pair but offered Jack a token apology all the same. It wasn't the first time she was glad to be his guardian instead of Miko's. He just nodded and returned the excuse for being late, though he didn't say too much on the ride back to the silo. Instead, he gripped her handles and squeezed her seat a little tighter than usual.

It seemed tensions were contagious, and after dealing with Ratchet's fretting over the dwindling energon reserves, she did the only free thing she could do. Head down to the sparring room and abuse a few of the weak training dummies. After slamming her heel down onto the back of another droid's head, she heard a clap from behind her.

"Remind me never to get you mad, Arcee," Jack said, climbing up the few stairs to the observation platform. The rusty targets were scattered across the concrete, and at least one of the internal batteries had become separated from the corresponding dummy. "Needed to vent?" "Best therapy you can think of." Arcee's intakes started to slow down, and she cooled off, relaxing her defensive position. Jack was taking in the sight of the dismembered dummies, but his posture was still straight and tense.

Arcee smirked and jutted her hip out, quirking an amused eyebrow at her partner. "If your wound up, you're welcome to have a go," she said, motioning with her servo towards the downed target.
" Who knows? You might be able to work out a few of those 'teenage frustrations' Miko is complaining about." Arcee turned to leave, but not before catching a look of absolute horror and shock on Jack's blushing face.

"You… have no idea what you just said…" It was quiet, but she still heard it. And even as she walked away, her satisfied strut lost its gait. It was meant to be a joke at her partner's lack of subtlety. Instead, she may have actually offended him. At the very least she embarrassed him. And he was right – she assumed teenage frustrations were the same as any other. She really didn't know what they were.

"C'mon Jack," she said, her voice softer as she stopped and beckoned behind her. "Let's go for a drive."

That night, Arcee was still mulling over Jack's words. Over the months she had known him his moods and attitudes were pretty reasonable. A little mischievous now and again, but brave and patient. The voice of reason. Ratchet was quite accurate when he pointed out the similarities between Jack and Orion Pax. Which made his embarrassment over her mistaken joke even more confusing. Surely it couldn't just be because of a phrase like "teenage frustrations."

Arcee was tempted to ask June privately if she had any insight, but "helicopter mom" as Miko called her already fretted over her son. And even Arcee knew that bringing the issue up with his mother would cause no end of humiliation, perhaps for all three of them. So after a steady and quiet drive, she parked herself inside the Darby's garage, bid them both a good night and radioed the silo for her ground bridge. With no fresh insight on the matter, she wound up in her quarters across her berth.

So what was the big deal about it all anyway? Jack was only young, and even with his shorter lifespan he still had years, decades in fact, to build his future. Have a romance, learn a career, start a family, etcetera etcetera. Even from a purely biological standpoint, the stresses of working and mating alone couldn't affect a sentient species that much… could it?

While Arcee had developed a more in-depth understanding of Earth and its customs since meeting Jack, she never considered learning more than what was necessary. If she had a question, it was just as easy to ask her partner on the spot. "Maybe it needs one of these doohickey's?" She was a fighter, not a researcher. But confronting Jack on his personal issues wasn't something she was planning anytime soon. And, she had to admit; even Bulkhead had managed to soak up the local customs more than she had…

So, with mixed feelings of curiosity and guilt, Arcee tapped into the world wide web and started picking apart information on the teenage mind. The mass of data focused less on the future and more on loud music, entertainment and surprisingly, romance. After briefly exploring the topic and rejecting poetry and 'making out' she decided to change tactics. She carefully culled the results down to focus on the male gender around Jack's age suffering 'frustration'. The results were almost as varied and staggering as her original search until she hit upon general information on a time of life called 'puberty'.

Maturity, hormones, changes in skin? The entire ordeal sounded excruciating, and Arcee couldn't help but pray silently that Miko would never enter the wild mood swings that some humans their age were starting to go through. "No wonder Jack's frustrated," she thought aloud. All things considered, she counted herself lucky that her partner was still his mostly responsible self. She was suddenly amazed humans didn't froth at the mouth and shed their skin during this 'puberty' nonsense. And while Jack was in the middle of this maturing, it looked like he might just be victim to his own growing pains.

"Still doesn't explain why a good workout wouldn't take his mind off things, though." She reasoned to herself. Before she dropped off the network, she decided to push further into her research and see if she couldn't pinpoint the exact cause of this entire mystery. Common frustrations, hormonal urges, the descriptions were a mixture of colourful and clinical. She still felt a tiny pang of guilt, like she was perhaps spying on Jack. Until her searching managed to focus on an earlier topic – human reproduction. Specifically, sexual frustration.

"Human's get worked up if they don't breed? Seriously?" That couldn't be right, surely. All species reproduced out of instinct. Even bonded cybertronians mated to reproduce protoforms. What could be so special about the act on this planet than any other? Arcee cleared her gathered data away, fighting curiosity for almost ten of the local seconds before taking one last plunge into the internet.

The sheer mass of information was overwhelming. This is what this 'sex' was all about? Physical stresses, mental static, stimulation, release, intimacy, lust, groaning, climax, tension, wetness, stroking, friction, euphoria…

"Wow…"

Sure, she had experienced these sensations before with others in her life, but never to the degree that humans apparently did. Probably not as carnal and raw, and not all at the same time, either. Arcee picked at the information until highlights began to repeat themselves, and with a detached feeling she disconnected from the web and relaxed into her recharge berth. The rest of the night was spent mulling over the data she had gathered and remembering how his legs squeezed her seat tighter than normal that day. Just how much of all this data applied to her partner?

"Who knew humans had so much fun…?"

A few days after her initial fact-finding, Arcee was back to abusing the remaining pair of training dummies. (As Ratchet would need to reinforce the joints and battery housing of her last victim, and more work was the one thing he didn't need.) A stiff, rusty hand landed on her shoulder, and she pulled the target forward harshly. It had been days of quiet boredom, with no Decepticon activity. With little to do, Arcee had more free time to sit and think. And, ultimately, her thoughts would wander back to her online discovery. 'Just how much could you learn about that stuff online, anyway?' she thought.

"I always learn so much from up here," came a voice, and she was almost startled to see Jack leaning against the platform railing watching her. "Like 'never come up from behind you' and 'how to tear an arm off in seven seconds.'" Arcee rolled her optics and smirked, mentally laughing at the idea that he had somehow been reading her mind.
"Don't get on my bad side. It's a lesson most 'con's learn just the once." For the nth time that day she wished a few Vehicons would need a reminder lesson – suddenly being alone with her partner and her new insight was causing an itch in her spark.

Instead, she went to leave the training room and beckoned after her."C'mon partner, let's go get some air. I think I'm starting to go stir crazy." Jack soon fell into place beside her, and they wandered through the silo.
"You should get a hobby, Arcee. How about music?" A sudden image of Bulkhead and Miko "rocking out" entered her mind and she shook it clear.
"Pass."
"Okay, not music… how about TV? Soak up some of the culture?" She hummed at that one in thought. Most of her television experiences were of Bumblebee and Raf watching cartoons.
"Still not a fan of Saturday Disney, Jack."
"Reading then." And again, she was assaulted by her newfound information. Things like biting necks to satisfy primal urges and sensitive organs moving against each other. 'Oh, I've done my fair share of reading lately, thank you.'"I don't remember seeing you do any of these things when you're bored out of your mind, Jack." The teen just grinned up at her.
"I'm in the middle of an alien war – kinda forgot what boredom is at this point."

"Well, you're lucky. At least if you get worked up, you can just…" Arcee suddenly trailed off, feeling suddenly trapped and looking away. Had this curiosity really developed to the point where it was influencing her actions?
"Sorry… what did you just say?" 'I've started, may as well finish…' she thought to herself.
"…you can take care of it yourself." It was a mumble but she said it all the same.
"Wait, wait… what are we talking about?" Jack had stopped short in the hallway and looked confused. "It's like your… are you suggesting…? No, you can't be…" Jack shook his head and looked as though he had almost admitted to being guilty of indecent thoughts. Arcee puckered her lips and crossed her arms, looking away and forcing herself to sound casual.
"And what if I was suggesting it…?" She turned the corner and kept walking. She had gone and blurted it out, but keeping it bottled up inside was starting to become unbearable. Wasn't all this supposed to be a big thing on this planet? Primus knows there was enough data on it – why was discussing it such a big deal? Excitement, building tension and releasing it with someone… wasn't all that supposed to be good?

Jack jogged after her, face heated and staring at her. "Arcee, do you really know what you're talking about?" The blue femme stopped in her tracks and tensed. She suddenly wasn't sure about anything on Earth anymore, and it was going to drive her mad until she made sense of it. She marched towards a nearby hatch and shoved it open, stepping inside an empty room. She had to wait longer than she cared for Jack to follow awkwardly, and she slid the heavy door shut quickly.

"Okay, so talk." She crossed her arms over her chest as Jack seemed to be caught between saying two things at once.
"It's… well… it's private," he finally said, and her conflicted data was beginning to annoy her.
"Then why is there so much information on it? For something so private, people sure as scrap don't mind talking about it." The blue femme planted herself on the ground, one leg stretched out as she thought quickly. All of her enlightening intel was useless, it seemed.
"Arcee, I… I gotta ask," Jack was still blushing, but still looking up at her face as he spoke. "Why are you even so curious about all this? I wouldn't have guessed this… topic was your interest."

It was Arcee's turn to grow shy suddenly, and she looked down and away for a moment. What had started off trying to understand her best human friend better was building into an infatuation with his biology. And despite knowing that she was entirely out of line with it all, she just couldn't bring herself to stop now. After all, it wasn't painful to Jack. 'Far from it,' she thought, before turning back to him.

"Well, I guess with all the different ways you can… I just find it a little… fascinating."
"Fascinating?" For a moment, Jack felt like he was suddenly an observed specimen, especially with the way she was staring at him so intently with her aperture optics. But Arcee was mulling over her gathered data again. Ideas about euphoria and excitement and the implied trust between people who let themselves be that intimate with others.
"Yeah… fascinating."

Jack looked torn for a long time, feet planted and beginning to say something before closing his mouth. It didn't help that she continued to watch him, her head tilted slightly to the side. Inside he was a whirlwind – embarrassed and heated, and somehow already feeling exposed. But the rush of hormonal excitement was slowly growing. And her own look of curiosity was only adding to the entire ordeal. Finally, he slowly moved in front of her and tapped her other leg with his.

"Straighten this for me?" Arcee cocked her head but straightened her legs out regardless.
"Sure… why?" Jack could hear the genuine surprise in her voice, and he could only bring himself to glance up at her."You want to know more, and I want to be comfortable," he said, as he turned around and planted himself as she had done. 'And I'm not sure I could watch you watch me…,' he thought, pressing his back against her body and breathing deeply.

Arcee bent her knees up and let Jack settle between her legs. Together she could only mildly notice that his hair brushed underneath her armoured chest, and she leaned against him gently. Even then, the tenseness in his body was evident, and he was hesitating. When it was clear he wasn't sure what to do next, she placed her servo on the back of his shoulder and rubbed slowly. Maybe she was being selfish after all?

"Jack… if you don't want to show me…""No… it's okay." He leaned into her touch slowly before breathing strongly and reaching downwards. Arcee couldn't help but watch as he slowly pushed his jeans open and down before untucking himself. A firm, aroused length that stood out, pointing upwards. He froze up a moment later, and she remembered all too late just what exposing himself to her implied. The situation suddenly struck her dumb, and all she could do was hitch her legs up closer to him. She settled her body tighter against his tense back, rubbing her thumb across the spine of his neck. Jack seemed to relax just a fraction, and while keeping his eyes anywhere on the empty room around them, reached down and gripped himself, groaning softly.

Arcee could only stare down over Jack's shoulder with rapt attention. The length, the shape, the wet slickness growing at the tip. A barrage of little thoughts ran through her processor of the mechanics involved in human reproduction. But mostly she saw the way his hand stroked and moved over himself, the flush in his face and thumping heartbeat. The sharper breaths and feeling him push back further against her. And the hot thrill of excitement in her spark at knowing just how intimate and private the entire act was. And he was doing it all for her because she asked. Her fingertips slid down his back, and she pressed against him, her thighs pressing against his hips gently like he squeezed her seat.
"Jack…"

His hand sped up and he tensed against her, freezing for a moment. Instantly the femme thought she had done something wrong, but instead, Jack hissed out sharply and leaned back between her legs."Arcee…!" And she watched his hardened organ swell and twitch before shooting a pale fluid. Jack's hand moved to grip her thigh as more thick drops landed on the floor in front of them. Finally, the teen began to relax against her, face flushed and breathing hard. Arcee felt her own intakes breathing deeply to try and cool her down. The entire show filled her with excitement and interest, watching him pleasure himself. But the desperate use of her name as he came was the most erotic thing she had ever witnessed.

Arcee watched as Jack quickly tucked and covered himself up, running a hand through his hair and catching his breath. He still hadn't looked at her since agreeing to show her what was involved in "taking care of it yourself." The fact that she had noticed herself, and she felt a small fear and doubt creep into her spark. He stood on shaky legs after sitting on cold cement so long, but before he could move away, she crossed her feet in front of him. He slowly turned at looked up at her, blushing awkwardly. He opened his mouth for a second before closing it, and finally, she couldn't take it any longer.

Arcee slipped her servo across the back of his shoulders, pulling him a step closer in an awkward embrace."Thank you for sharing that with me," she said, cursing her embarrassed tone. But soon enough Jack's arm came up against her side.
"Sure, Arcee. Sure."