A/N:

Thanks to androidkisser on ao3 for suggesting tickle fights/pillow fights!

It had started innocently enough.

There was nothing out of the ordinary that morning, as he did her regular scheduled maintenance as usual. His voice echoing around inside her head, soothing against the somewhat uncomfortable feeling of him poking around in her code. Sometimes she had the thought that if he wasn't the one available to do this, she wouldn't trust anyone else enough to see and mess with everything that made up her entire being.

She trusted him to be careful and leave everything as it should be, and not a soul other than him.

He withdrew from her while her thoughts ran wild, and she wondered if he could ever see them inside her. She wondered what he thought, if he could. As his presence vanished and only his soothing voice stayed, going a little quieter as her other senses rushed back in, she felt the sudden and inexplicable urge to pull him back.

Not entirely aware of her own body as her control returned, she accidentally let that thought take over and move her, her arm shooting out suddenly to grab for 9S. But her coordination was off, and instead of firmly catching his hand, all she managed to do was graze his side.

A sound escaped him, then. A strange noise, almost a squeak, as he instinctively darted out of her reach, and she froze. She'd never heard him make such a sound before, and she couldn't quite put her finger on what it was or why he'd reacted in such a way.

She wanted to know more.

2B had sat up and brushed off the interaction, pretending nothing had happened as she swept past him to start their day. But it stayed on her mind, drifting back into her thoughts now and then anytime she looked at him. She kept hearing him squeak, and no matter how much she went over it, she could never find a reason for the scene.

And that's where they found themselves, now. It was late, hours since that moment in the morning, and she was still thinking about it. He was chattering on about something useless as they walked through the darkened forest, it seemed he had forgotten about the exchange entirely.

Her eyes trailed over and focused in on him, beside her. His face was split into a wide smile, and she realized he was talking excitedly about the behaviors of some animal they'd passed. She was sure that if his blindfold was off, she'd see his eyes sparkling with life, the way she'd seen before. If she didn't know better, sometimes she could have believed he was human.

"2B?" His voice changed, confusion and a little concern leaking into its tone. Only then did she snap out of her thoughts and realize she'd stopped, and was staring at him. "Is everything okay?"

She opened her mouth to reply, but closed it after a moment, realizing she had no words to explain. That morning was still bouncing around her head, leaving no room for any other thoughts. As her internal debate continued, she watched his concern deepen, and he reached for her.

His hand stopped just short of touching her shoulder, as if afraid to touch her without permission, but it was enough. As if pushed by a force that was not her own, her hands moved swiftly to snag the collar of his coat, and she watched his posture stiffen in surprise.

"What's wrong, 2B?"

Still she said nothing. Again her body moved without her entirely giving it permission to, and she pulled firmly to the side, tipping him slightly off balance and giving him no choice but to comply as she forced him to the ground. Despite her odd behavior and lack of response, 9S relaxed as his back hit the forest floor and she pinned him in place, nothing but pure trust on his face. There was a slight blush rising in his cheeks, especially once he realized her knees were on either side of his body and her hands were planted flat on his chest, but he stayed still and didn't turn into a flustered mess.

It seemed his curiosity was winning out over being flustered, for now. "What's on your mind, 2B? Not that I'm complaining, of course."

He expected no response, and that's exactly what he got. Slowly she moved one hand, trailing it up his neck, and he shivered as her fingers brushed ever so lightly on his skin. She was leaning forward, putting a little more weight on the hand remaining on his chest, but he didn't complain as he stared straight up into her unreadable expression. He was turning more and more red by the second, especially once she brushed her thumb over his lips and leaned down close enough for him to feel her breath. His words died in his throat completely now, only able to focus on her gentle touch, and her lips curled up in the tiniest hint of a smile at his silence.

But silence wasn't what she was looking for, at least not right now. She pulled away, leaving him a confused and flustered puddle as she sat upright. In the process she let her weight rest right on his hips, and he turned even more red if that was possible.

They stayed like that for a few moments, 9S trying to catch his racing heart and 2B watching him with barely hidden amusement as she debated what to do next. Despite what his flustered reaction would say, they were no strangers to this intimate dance of heated breath and teasing, but it wasn't quite the reaction she wanted to explore this time.

That didn't mean she couldn't have fun with him like this in the process, however.

She tilted her head innocently. "Nines?"

He cleared his throat nervously, and his voice came out slightly choked. "Y-yes?"

"I'd like to try something." Her voice was nearly a purr, and she was pretty sure he came within an inch of self destructing at that exact moment. "...Hold still, okay?"

Her hands went back to his chest, her gloves brushing the fabric of his coat as she pressed down gently. He felt strong and steady beneath her, despite his small frame otherwise making him look fragile. Trailing down, she felt his synthetic muscles as best she could through his coat, exploring the dips and ridges of his body all the way down. He turned to putty beneath her, his skin pushing back against her touch every time he breathed.

Finally she reached the hem of his coat, and her gloved hands found their way underneath with zero hesitation. He took in a sharp breath when he felt the smooth satin on his bare skin, and she pushed the fabric of his coat up as she explored back up the same muscles again. Again, he felt solid and sturdy beneath her touch, reminding her that he was built just as well as she was even if he wasn't made for fighting.

A few of the buttons on his coat came undone, giving her easier access as she gently massaged his skin. Her fingers trailed in circles up his chest, pressing into him enough to be soothing but not nearly enough to be uncomfortable. Though still flustered beyond belief, 9S was also turning to complete jelly under her relaxing touch.

She smirked, looking down at him. There wasn't a single tense muscle in his body where he lay on the uneven earth, and his chest rose and fell in breathless pants. He was completely and utterly at her mercy.

Stilling her massaging movements on his chest, her fingers took a sharp turn straight for his sides, still incredibly gentle but not nearly as pleasant as they grazed suddenly down his ribs. His reaction was instantaneous, a loud and startled squawk escaping him as he twisted underneath her, his own hands flying to grasp her wrists.

Looking up from his body to his face, she felt their eyes meet even through the blindfolds. His lips were parted, gasping. He looked like he wanted to say something, but couldn't quite decide what.

In fact, he looked as if he knew about as much about what was happening as she did.

She pressed down again, grazing her fingertips between his ribs. His body tensed, sitting up slightly as he curled in on himself and his grip on her wrists tightened. A choked sound escaped him.

"What… are you doing?" He managed to gasp out, looking up at her like a startled deer. Neither of them had any idea he had a weakness like this.

"I don't know." She wiggled her fingers further down his sides, ignoring his crushing grip on her and listening closely to his startled gasp. "What does it feel like?"

"It's… unpleasant." Relenting for a moment, she let him catch his breath. "It's not painful, just… weird?"

She hummed, and trailed her fingers much more gently back up his sides. He only tensed up under her touch, and made no noise. Then she feathered them back down again, wiggling her fingers on his skin ever so faintly, and this time he curled up completely to hide his face in her shoulder and made a sound that was remarkably similar to choked laughter. They both froze.

"Did you just laugh?"

"I think so?"

2B removed her hands from inside his coat, moving them to his shoulders and pushing him away to look at him. "I thought you said it was unpleasant?"

"It is!"

"Then why would you laugh?"

"I don't know!"

She stared down at him in silence.

"...You're going to do it again aren't you?" He asked, his voice full of disdain.

"We should investigate it, right?" She pointed out, her hands reaching for his blindfold. "What if it's a symptom of a virus?"

They both knew it was a possibility, but that it wasn't the real reason she wanted to keep doing it to him. She couldn't quite place why, but for some reason she found it… fun?

In an instant his blindfold was gone, and he was blinking up at her with those beautiful eyes, always so full of emotion and humanity. Something in them was different right now, he looked slightly uncomfortable but also somehow completely submissive to her prodding. The way his eyes caught the light as they stared up at her, it was almost as if he was saying he'd let her do anything as long as it made her happy.

She suddenly felt a little bad for picking on him so much. He was being so patient with her curiosity, despite it making him uncomfortable.

A few moments passed, until finally she pulled her own blindfold off and looked down at him with such a soft expression, startling him slightly. "2B?" He asked, blinking.

Saying nothing, she just reached for his neck again, her fingers curling gently against the back of his head as she pulled him close and pressed their lips together. He took a sharp breath and reached for her as well, his hands grasping at her waist and digging into her dress.

Forgetting for a moment what they were trying to investigate, she pinned him back down against the ground. He gave not a single complaint when she pushed him flat, only tightening his grip and pulling her right down with him. It was only when his hands trailed back over her curves and down to grasp her thighs that she pulled away, breathing heavily.

"9S, we don't have to do anything you aren't okay with." She spoke with finality, making it clear that the choice was his. As much as she was curious about his strange reaction, she didn't want to hurt him.

It took him several moments to come back to the same page and realize what she was talking about, during which time she continued.

"We can do something else with our privacy if you're uncomfortable."

"Um…" He didn't miss her not so subtle offer, but truth be told, he was also curious. "Well… can I try it on you? Maybe it isn't just me."

She sat straight upright, looking down at him. She hadn't actually considered if it was something that affected her as well. "Hmmm…" Putting her own hands on her sides where she had on him, and experiencing no reaction, she looked at him again.

"Maybe it has to be someone else?" He offered. She only shrugged in response, and moved her arms out of the way, inviting him to try.

9S watched her face carefully as he tentatively reached out, watching her uncovered eyes closely. Her expression was level and composed as always, her gaze inviting, and it didn't change when he settled flat palms on her sides. He looked back up at her, unsure. "Move your hands, like I did." She encouraged, and he trailed his touch down, slowly turning to grazing his fingers down her ribs like she'd done to him.

Her reaction, surprisingly, was exactly like his. Her eyes squeezed shut and her arms crossed defensively as she curled in on her middle, a choked giggle escaping her. When she didn't tell him to stop, he continued, wiggling his fingers back up again, and she let out a true laugh as she desperately grabbed for his hands. Spurred on still, he didn't let her grip on his wrists stop him, partially because if she'd really wanted him to stop he wouldn't have been able to move them at all.

Grazing back down and digging his fingers into her sides, 2B trembled and fell over him as she curled up completely, her laughter filling the area. 9S felt his face split into a wide grin and he flipped them over, pinning 2B to the ground instead as he continued his assault. She made an incredibly girly sound when she hit the ground, her giggles continuing but starting to sound strained and breathless, and she hit his shoulder weakly as she flailed under him.

"N-Ni-Nines." Her voice sounded completely defeated and breathless, with an undertone of amusement as she begged for mercy. 9S felt his knees go weak at the sound of her pleading voice speaking his nickname, and he stopped suddenly from pure shock.

Finally released from his attack, she collapsed back against the ground and breathed heavily. He could only watch, completely enthralled as she relaxed against the ground under him, her eyes shut comfortably and her chest rising and falling as she caught her breath. Unable to resist, he slowly reached down, pressing a palm against the flat spot right underneath her collar and feeling her rushed heartbeat through her dress and skin.

Her eyes opened slowly, frosty blue watching back up at him through half lids, and she smiled. "You should see yourself right now. You look like you just saw something amazing."

His mouth opened and words fell out.

"I did. I saw you." Realizing what he said, he trailed off, mumbling. "And heard you, and… wow."

Under his hand, her heartbeat sped up. Her eyes grew ever so slightly wider, and finally she looked away, as if embarrassed.

"Hey, 2B?"

Her gaze fell back on him, silently questioning.

"Thank you for… whatever this was. For letting me try that on you too."

"Anything for you, Nines."

And if he realized, as she pulled him down to her again, that he had finally gotten to listen to her laugh so freely, he said not a word.

A/N:

Sorry about how long it took to write this one, work has been crazy and I had some cosplay stuff to do. Let's see if I can get back into the swing of things here!

Also, this wasn't quite what I imagined initially for this prompt, I feel like it doesn't quite stay true to 'tickle fight' because it's more them exploring their bodies together. To make up for it I may do the other half of the prompt later, and write a pillow fight fic? Let me know your thoughts and leave your suggestions for future prompts as always!