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Let’s Experiment!

Summary:

Law takes a girl home for experimental purposes after learning she was on her period. Turns out she’s actually a he and he really likes him.

He is so screwed.

Notes:

So- this is the- what- second time I wrote smut, but the first time it’s EXPLICITLY SMUT. So like- go easy on me. I think this the longest fic I’ve written yet and honestly, this might become an au because I have so many ideas for this verse. I apologize for any oocness but I was having fun.

(Yes, I will finish Wings and servos, I just decided to have a well deserved break.)

Edit: 1/28/26 I wanted to fix some parts and FINALLY italicized the thoughts.

Edit 2: 2/5/26 I fixed some grammar mistakes and some inconsistencies I saw.

But other than that, have fun, comment and pls don’t flame me 😭

Work Text:

Law closed his bedroom door and twisted the knob until he heard a click. Finally, he thought as he turned to gaze upon the girl on his bed. I have my first test subject! Excitement ran down his skin like a zap of electricity, he tamped down his almost manic grin into a confident smirk. “Are you comfortable?” He asked, he had to make sure.

The girl looked at him through her flame red hair, her equally red (or were they amber?) eyes that were just as striking. Red, red, red, I just love that color, not more than yellow but- “enough, I’m just… having second thoughts.” The girl said, interrupting his train of thought. She turned away from him, bringing her knees up to her face. 

The boy just sighed, taking off his jacket as he moved towards his closet. “Why? We made a deal, remember?” He reminded the girl, grabbing a hanger from the pole. As Law was putting the hanger through the neck of his jacket, he sneaked a glance at the girl. 

Figarland Elspeth, as mentioned earlier, had red hair and amber red eyes, pale skin and a permanent frown that always looked odd on her. 

His eyes traveled lower to the way her legs were positioned. It was a sight to behold really, Law could see what kind (and color) painties she was wearing. 

Yellow.

Flowers.

Neat

The leggings weren’t even doing a good job of covering her up either. His dick twitched at the thought of him taking them off and- wait no. This is an experiment, not a pleasure seeking venture. There was a reason why Law waited for Cora to be at work to invite Figarland-ya over.(With permission to do so from the man of course.) 

He hadn’t expected anything, because it was under the pretense of studying and Cora knew how serious Law is about school work… it just worked to his favor when he lied about it too. 

With a smile, Law hung up his coat and turned to Elspeth. She still hid her face with her knees. When he sat down beside her, she finally spoke up. “I know we made a deal… but… no one asked if- if they could-“ she struggled to say the words. “If they could eat you out?” Law finished for her, a little confused now. Doesn’t Killer get laid like, all the time? He’s Elspeth’s best friend so she should know by now… right? (He’s right but Elspeth is a virgin, her brothers, made it incredibly difficult for her to even have a boyfriend.)

Before Law could ask however, Ellie (Elspeth) was already grabbing him by the collar shaking him. “Not that dumbass!! First of all, I’m in your house! Second, YOU want to eat me out while I’m on MY PERIOD! Do you know how GROSS that is?!” The boy was barely listening, he was too busy staring at Elspeth’s flushed face and bared teeth. 

She looks so cute when she’s mad. 

“Exactly, Figarland-ya, as a future doctor, I need to experience all the gross stuff. Hell, I think I’ll experience more blood during surgery than eating you out.” He waved around his hand back and forth in a rather blasé way. “I mean, I said I was already going to pay twenty bucks too.” She at least had the nerve to look embarrassed by that.

 “But… I don’t- I- I haven’t even done it with someone...” The girl trailed off, the blush growing down her face and down her neck and towards her chest. From this angle, Law can see Ellie’s intermammary cleft. “We don’t have to do it, I just want to know if period blood tastes different from ACTUAL blood.” He pokes the girl in the forehead, who huffs. Well, he’s not sure on that part but he knows for sure he wants to taste it.

Law continues poking her head as he said “That and orgasms can help your period cramps by triggering the release of endorphins,” Ellie gave him a look, already annoyed by his poking and he knows that his ramblings bore her to no end, but he doesn’t really care at the moment because the next part WILL catch her attention. 

“These natural painkillers boost mood and reduce pain, allowing the uterine contractions that help expel the lining go faster. Which can potentially shorten your period.” 

And. 

Law was right. 

Elspeth immediately perked up at the last sentence. “Shorten… my period?” She lets go of Law’s shirt, who grins. “Yup.” He said, popping the p. Law almost couldn’t help himself when he inched closer to her. “You’ll also get like, twenty dollars out of it too, so really this is a win, win, WIN, situation for you.” Law had his hand inch for Ellie’s thigh, but what she asked next made him pause. 

“What is that third win?” Law leaned into her space, their faces now inches away from each other. “You will feel good. Now, take off everything below your shirt. I’m going to get my equipment.” She looked at him for a moment before she nodded. She’s been convinced! Victory!

Smiling, Law patted her shoulder before he got off the bed and padded over to his desk. 

Gloves?

Check. 

Vials? 

Check. 

He didn’t want to use any of the other stuff on her but he does want to collect some of her blood and run some tests to see how periods are different from what you can find in your veins. Figarland-ya stood up and was taking off those leggings, her skirt, and… the panties were yellow. Not just any yellow. 

Canary Yellow.

His favorite yellow.

That’s his favorite color, he liked that she was wearing his favorite color. It did things to him. A blush flushed down his neck as he quickly turned away to give the girl behind him at least a modicum of privacy. Oh, she was wearing my color this is bad-

The boy did his best not to think with his dick but with his mind, however, this was proving to be difficult. Law stared at the garments, dragging his eyes away from the yellow underwear, particularly the menstrual pad that was attached to them. “Can I have that?” With a sigh, the girl nodded. Law took the pad from her underwear and wrapped it up with a paper towel. The girl then said, “Could there be a towel under me at least? I don’t want to stain your bed.” She had a point, Cora would become instantly suspicious if he found blood on Law’s bed covers… again. 

“Of course, let me get one.” He got up and grabbed his own personal towel from the floor and folded it twice before laying it on his bed. Figarland-ya regarded him for a second before sitting down. Law subconsciously licked his lips before crouching down. “Can you spread your legs for me?” Almost immediately his request was answered. 

However, before he could even touch the specimen she grabbed his shoulders. “If we’re actually going through with this, I have a request and… I’ll trade out the money for it…” Her voice was so small. Law raised an eyebrow, but he could see the apprehension in her gaze.

 “What.” 

Figarland-ya swallowed before looking down. “C-call me Kidd and u-“ she took a deep breath, regulating her nervous system. “And use he/him pronouns for me. Please.” 

Oh

Law thought it was to destroy the evidence but that’s something he can do. At least, he hoped he could. “Sure. Now lean back. I wanna see your pussy.” Figarland-ya was now on her back, her slit now on display. Wiry, red pubic hair greeted Law as he put a gloved finger against the slit. Figarland-ya tensed up but relaxed. The slit also moved, opening just slightly against his touch. “You have a wonderful organ, F- Kidd-ya.” He tested the name against his tongue. 

It was weird, but honestly, Law didn’t care that much. He didn’t know why Figarland-ya wanted to be called Kidd or why she wanted to use male pronouns. He didn’t know her or her issues and he didn’t care enough about them. (Sure.) For now at least, he just wants to eat her out. 

Law leaned in closer and breathed her in, the copper smell was very strong as well as the musky smell of her sex. Elspeth shivered beneath him, she’s tense again. Law rubbed her thighs before licking her slit. It was like drinking blood, but sweeter. Her breath hitched at the feeling.

Figarland-ya is making so many debauched noises! Her- or should I say his? I should start referring to him as a he, right? Ugh, why does she have to be so complicated? No, why does HE have to be so complicated? 

At least he tastes good. I can feel his hands are digging into my hair, I don’t even know where my hat is. His vaginal fluids mix so well with the blood, it’s almost like… an aphrodisiac. 

“Law- Law- please uh- can get up a little higher please- ah!” Kidd yelped- grabbing a fistful of Law’s hair. The boy’s tongue was diving in between the folds of Kidd’s sex before brushing over his clit before going back to the folds. He was becoming a little too engrossed, Law shifted the both of them to where Kidd’s butt was in the air and his toes were barely on the bed. Law was on his knees, leaning heavily against his mattress as his hips made small little gyrations against it. His dick was actually aching, this is insane.

Can someone come from soft moans alone? Law then dragged his tongue across Kidd’s labia before landing on his clitoris. It was engorged and swollen. Minutely twitching beneath his tongue, almost like it had a heart beat. Kidd was also turned on, how wonderful. 

“Yes- yes Law- yes please-“ Law surged forward- he loved that word! Please- he wants to hear more of it. 

“Say that again.” He groans, gripping Kidd’s hips. “What word?” Kidd whined, an edge in his voice. “The last one dumbass, or I won’t continue.” Law retorts. He was bluffing of course, no way he wasn’t going to stop. The look of fear that flashed in Kidd’s eyes though, gave him an odd sense of pleasure and maybe power. But what Kidd had said next made Law lose the ability to breathe.

His head was against Law’s pillows, his red hair fanning behind him like bloody viscera, while in the sluttiest voice a fifteen year old can muster (to Law, who was sixteen by the way) “please Law, I need it, I-I want you to eat me up.” His voice was soft it was like silk draped against a hard edge about to rip. Law would replay those words for the rest of his life, he finally got her- HIM to say it. Law just didn’t expect his prompting to work.

“Oh baby-“ Law sighed, lust now finally filling his systems. Kidd squeaks when Law clambered onto the bed, ripping the plastic gloves off his hands with his teeth before removing his shirt. “I wanna do more than that.” The black haired boy finished with a rather lascivious grin. It looked downright devilish. Kidd almost balked when Law began undoing his belt. “Hey! You said you were just going to eat me out!” He squeaked, pushing the other boy away just slightly. This isn’t what he signed up for despite the way his slit begged for it

Law rolled his eyes. “It’s not that different!” 

(Yes it is, it totally is, don’t believe this selfish brat.) 

Kidd shook his head and crossed his arms. “No.” Law wanted to scream and cry, his dick was so hard he was sure the zipper would leave imprints! And he was wearing underwear! But most importantly he wanted to be in that slicky warmth! 

“But why?” Law almost whined. He was now directly over Kidd bracketing him with his arms. At this moment Kidd must have taken pity on him because the… boy, yes the boy uncrossed his arms and hesitantly brought Law closer. “I just… I haven’t had sex before…” Kidd blushes heavily, her- his cheeks were so pink.  “I know…” Law responds softly, his response coaxing the red head to continue. The boy below him paused before averting his gaze and continuing his confession.

“I also really really like you.”

 Oh shit.

Now Law felt like a bastard. 

This was supposed to be an experiment, to play with the female body (with the participants consent of course.) Maybe he shouldn’t have chosen Kidd for this but how would he notice that Kidd liked him in the first place? 

Damn… 

well… 

Law never thought he would get the opportunity to have an almost permanent specimen but the least he could do for the other boy was to reciprocate his feelings. “I wouldn’t want to fuck you if I didn’t like you, Figarland-ya.” He said softly, capturing Kidd’s lips with his own. The surprised gasp from the boy made something bloom in his chest, it felt like fire and it flowed down his chest and towards his stomach. 

The lie tasted almost bitter but Kidd was so sweet. When Law pulled back Kidd’s eyes were glassy almost like he was about to cry. “You mean it?” He whispered, bringing his hands up to touch his face. Law didn’t even hesitate. “Yes.” 

Kidd bit his lip before looking over to Law’s shoulder and towards his desk. “It’s four thirty, do you still-“ before Kidd could continue Law interrupted almost desperately. “Yes please!” Cora doesn’t come home until six thirty anyway, which means they have a lot of time. “O-okay then, just be gentle. I really didn’t think…” Law didn’t hear the rest, his mind already trying to come up with reasons for why sex had become a part of this.

Maybe this could be an experiment of endurance as well… 

He quickly gave up on that venture.

Oh, who am I  kidding, this is fun. I should play with her- him, him… We can make this fun for each other.

Already, Law could feel the dried blood stretch across his face and judging Kidd’s reaction when he jostled his hips, it hurt. “Ow.” He whimpered but Law was off the bed again, mouth to clit. That whimper turned into a moan. This time, Law was palming his dick, giving it the friction it so desperately needed. He didn’t want to pull it out just yet, as it would be a little too dry to pump himself comfortably, but Kidd-ya will give him a helping hand. 

Licking circles around his clit, Law raised his hand to press a couple fingers on the folds, Kidd flinched as a drop of blood slipped in between the folds and coats Law’s fingers. It encourages the other boy to gently press into the slick hole. It was so warm and slippery! “Kidd, you’re amazing-“ Law praised again as he pulled out there was a membrane like substance on his finger. Curiosity killed the cat as they say so he ate the substance. 

It tasted like nothing but something at the same time. A little slimey but interesting. Chewy. With the intense need for more, as the cat was satisfied and was brought back. Law spread the folds of the red head’s cunt, it was already so bloody. He then began lapping it up like a thirsty dog, the squeals the other boy produced only added to the experience.

“Law! Law- Law- Law-“ he was chanting his name again. And then, before Law could react Kidd yanked his head down, pressing his face harshly against his sex with a keening moan. His thighs clenched around his head like a vice. 

“Fuck.” Neither boy knew who said it, just that it was the collective consensus.

 (Kidd said it because Law couldn’t.)

I made him come with my mouth, wow-

Now Law felt spectacularly neglected, his dick was aching something fierce. The black haired boy trailed a hand down his pants again, unbuckling the belt and unbuttoning his pants before pulling out his dick. “Kidd-ya come over here” with a hiccup, Kidd leaned over, tears staining his face. 

“Can you open your mouth please?” The way Kidd licked his lips made Law’s dick throb and he opened his mouth just as he should. 

It’s honestly so hot. 

Can sex make you catch feelings or was it because Kidd was on his period? 

Did periods have bewitching powers on men?! 

The words sounded ridiculous but Law couldn’t help but think them, it’s how he felt.

With a shaking hand, Law slipped two fingers in Kidd’s waiting mouth. 

His mouth was about as wet as his pussy. The muscle that was his tongue rolled around Law’s fingers, coating them with the saliva he needed. 

Because he wanted to, Law stuck another finger in Kidd’s mouth, making them both moan at the sensation. The way his face heated up and his eyes were just pinned on Law like he held up the sky. It sent a tingling sensation down and into his gut. 

Licking his lips (again-) Law pulled his fingers back and began to stroke himself with the wet fingers. Once he was a full mast, he climbed onto the bed. They stared at each other for a moment before Kidd held out his arms. Law obliged the request, hugging him back. 

He smelled sweaty and bloody, in fact, they both did. Law then pulled back, going in between the younger boy. Kidd looked at him expectantly as Law began to slide his dick along that wet pussy. So soft and yet foreign. He entered without ceremony, which was right to the hilt, making Kidd yelp. 

Right, she hadn’t had sex before, I mean, technically neither did he- but man did Kidd feel good! He was so hot and plush, Law could stay here forever and be happy. 

“Ah-h.” Law couldn’t help but utter, Kidd was also breathing hard, the sudden intrusion was a bit more painful than expected. Their connection was a feeling that laced up between them like flames, licking every part where their flesh met. 

For Law, it was pleasure, his girth was being squeezed rhythmically to the point he couldn’t sit still. But, if he moved he would come almost immediately. 

For Kidd, it was more pain than pleasant, the thing inside him twitched it jumbled his nerves in tandem with his muscles tensing and then un-tensing in a heart beat like rhythm. 

It was when Kidd jerked up his hips and made a quiet “move” for Law to process his plea. “O-okay.” Slowly, ever so slowly, Law began to pull back (and oh god there was blood on his cock) and push back into Kidd again. It was the sensation they were after, it rippled with pleasure and pain as Law grabbed ahold of Kidd’s waist before he began to fuck him in a moderate rhythm. 

Blood began to bubble at where they joined, and the bed creaked continuously at their consistent movements. Law pushed up Kidd’s shirt, and slid a hand under the bra he wore. His tits were a nice size, the black haired boy thought as he played with the mound with his hand. When he teased a nipple with his fingers, Kidd removed his hand swiftly from her-his! Goddamn it, his shirt. “Don’t touch me there, I don’t like it.” Is all the red head said before leaning back on the pillow and turning his head to the side, his face pinched with content bliss. “Oh… okay, sorry.” 

Law was disappointed, but heeded the others' demand. For some reason, he didn’t want to push Kidd, he wanted this to feel good for both of them. 

(He didn’t know why this feeling persisted, it felt like something akin to the lust drenching his bones but it felt primal. Older.) 

It was then, Law had hit at a certain angle that had caused the redhead to buck up and arch his back. It was like he was seizing his mouth open in a shocked gasp. Did he hit his sweet spot? Kidd then grabbed Law by his neck and held him close. “Again, do that again.” He begged breathlessly, instead Law kissed him. He didn’t know how to do it again.

Grinding his dick into the quivering cavern, Law stole Kidd’s breath away. He didn’t know how to kiss with tongue. All his experience with this stuff came from explicit movies and catching seniors in the act in the bathroom at school. But all of this feels better. 

It was almost overwhelming. 

Law forced himself to stop kissing Kidd, his lips were swollen with use. With hazy eyes, Law gazed up at the red head to find him crying. 

“Why are you crying?” 

Oh no, is this- 

“It's because I’m happy.” The words washed away Law’s worries like rain. Kidd gave him a wobbly smile. “I’m so, so happy. You love me…” that almost made Law stop, the guilt was back again, gnawing at him like a beast. But this time he actually thought about it. He had a knife to combat this beast, it was that primal urge again.

Law gathered Kidd’s legs and held them up before rolling his hips into the other boy experimentally. The redhead cried out, grabbing onto one his legs if only to hold Law’s fingers while he fondled himself with the other. 

Do I really love Kidd? 

I barely even knew him, didn’t even know he was a he before he told me. He was just the quiet girl in class who only hung around one person, Killer, the reason why they even know each other in the first place.

And Elspeth? Was that even the right word to describe the boy below him? Is he really chosen by God? If so, what was he chosen for? 

As Law continues to fuck the boy a little bit harder, the bubble in his stomach cresting, his thoughts began to circle. 

That name did not suit him. It’s a nice name but it’s too… weak almost. And it’s ugly whereas he is pretty, I wonder if he’ll be handsome when we grow older. 

I wonder if he’ll participate in more of my experiments. 

That line of thinking brought up an image of a more masculine Kidd, a buffer build with his hair shorter and a brighter more confident smile. The image made him consider, if not for a second. 

“I… would not be opposed to falling in love with you, Kidd-ya, not at all…” 

Did this negate his earlier statement? Yes, but did he bring truth to the lie? Also yes, he has defeated the beast, bloody and yet victorious. The primal feeling had a word to describe it but it was at the tip of his tongue. He couldn’t remember it. 

(Love.)

Law hadn’t meant to say the last part out loud for the red head to hear but the wet noise Kidd made had almost sent him over the edge. 

Pulling out as fast as he could, the black haired boy let go of the pale legs and pulled up Kidd’s shirt before stroking his dick as fast as he could. Eye-fucking the other boy’s body as the red head was masturbating with him in tandem.

When the knots in their stomachs had finally ceased, cum began to cover Kidd’s chest in white streaks, whereas blood and pearlescent release soaked Law’s jeans. 

They were both whimpering from overstimulation and somewhat exhaustion, Law took a moment to breathe as he laid his forehead against Kidd’s. He stared into those glassy, wine red eyes. 

“I think we should stay together forever.” He said after taking a deep breath of fresh air. 

Before Kidd could respond to that, the sound of a car door slamming and a beep of a car instantly snapped them out of their post coitus reverie. “SHIT- what time is it?!” Law asked, frantically looking for the clock. 

It was five forty nine. 

Oh fuuuuuccckkkkkk. 

Cora was home early! 

Law instantly got up from the bed and went to look for some clean clothes, he can’t be caught dead in these jeans. Kidd winced as he got up from his laying position. “Do you have any pads?” Law turned to him and nodded, too busy taking off his jeans. 

Holy shit, his legs are STAINED. The sight almost made Law smile like a mad man. “Where?” Kidd asked as he got off the bed. The black haired boy watched as the red head’s shirt fell slightly, stuck to the cum that was now drying on his skin. 

“We need to clean ourselves with soap and a cloth, or else we will reek of sex.” He did not want to explain that to Cora-San, the embarrassment might kill him his benefactor’s lecture’s won’t. (And blood but that was not important) he quickly took off Kidd’s shirt and tossed it with his jeans before grabbing the boy by the hand and dragged him to his dresser. He crouched to find a towel and some cleaning wipes. 

“Law! I’m home!” Cora called out from the living room. Fuck, he can already hear the man climb up the STAIRS. 

Kidd quickly grabbed the cleaning wipes from Law and began cleaning himself down. “I have blood literally dripping everywhere, I need to clean myself off first.” He said rather succinctly. 

Right. 

Actively having a period. 

Gotcha. 

Law stood up and grabbed a towel, rubbing at his legs before walking over to his bed and grabbing the now really bloody towel from it. Before he left however, he spotted the sight of those yellow panties, with a quick glance, he made sure Kidd was busy before leaning down and grabbing the pair of underwear. 

He stuffed them under his pillow. 

The black haired boy then gathered up their bloody and or messy clothes, and put them in his closet. “Am I going to get that shirt back?” Kidd asked, pointing at the door. “Yeah, I just need to wash it. Now would you like to wear one of my shirts?” Law answered him before pointing at the open dresser. 

The redhead brightened at that and nodded his head enthusiastically. He chose one of Law’s least favorites, a brown and pink patterned one with a heart for a pocket. Before, Kidd could ask again, Law bequeathed him a pad and a pair of boxers. “Uhh I already have underwear. But thanks.” Kidd tried to say but the other boy insisted. 

Law made a show by looking at the skirt and leggings by the bed. “I don’t see them.” At those words, Kidd followed his gaze and made a questioning noise. 

However, before the red head could take a proper look around, a knock could be heard from outside of Law’s door. 

“Law? You haven’t answered me, is everything alright?” The black haired boy was quick to answer, he was already pulling up a pair of clean jeans after he put on his shirt from before. “Yeah we’re cool! Ki-Elspeth-ya and I just had an incident with some sodas and we’re cleaning it up right now.” It was best not to call Kidd by his chosen name unless he said so. The grateful smile sent his way confirmed his foresight. 

That smile is doing funny things to me.

A long suffering sigh could be heard from the other side of the door. “Law, what did I say about having sweet drinks in the bedroom…”

As Kidd listened to their banter, he sighed as he put on the boxers with the pad tucked comfortably in it. He wondered where those panties went, they were his most comfortable pair. Oh well, at least he was wearing Law’s clothes… it was so nice of him to offer. The boy smiled to himself as he tugged the leggings and skirt on. At least he finally had an excuse to wear boy clothes. 

His hopefully boyfriend’s clothes. 

Killer could be wrong this time, he likes me. Hehe.

The thought made him giddy, lit up with a light feeling akin to butterflies. Kidd gave Law the all clear with a thumbs up and a smile, the black haired boy returned it with a chuckle before he opened the door, greeting Law’s benefactor. 

As the two left the room, the pair of yellow and flowered panties peaked out of Law’s pillow, somewhat forgotten. However, it will be removed from its hiding spot later that night, with its new owner looking at it with a smile. 

Yellow is his favorite color after all.