Archive of Our Own ^beta

Chapter Text

You lived in a large flat shared with your step-brother in Tokyo. His father was extremely rich and had taken you in after your father died from an overdose and your mom ran away. To be fair, it was a pretty traumatic upbringing, but he cared for you as much as he cared for Reo.

Your dad was never really here, wanted for theft and arson along with illegal drug use, and your mom had married the CEO of Mikage Corps soon after your dad was found dead. As much as you could see he cared for her, she was mentally unstable and still traumatized from her last relationship; to the point she ran away from home when you were 16.

A/N: This is set in the BLLK universe before blue lock! Reo’s mom divorced his dad for unknown reasons ( the money obv ) bc I don’t have time to give him a tragic backstory as well.

Since then, you lived with Reo on the 56th floor of some immense skyscraper as his dad, who you thought of as a father figure as well, was often away for business affairs. Not that you were complaining, since it meant you could afford, well, anything. And you’d be lying if you said you didn’t enjoy bunking with Reo. That is, more than you should be.

The purple-haired boy came into your life when you were 15, a promise of a new, less tragic life with his father. You’d instantly hit it off and became friends. Considering you were both only children, you’d never know the true strength of a sibling bond, but what you two had was enough and it made you happy. You’d always thought that he was like a sibling to you until he brought a girlfriend home one day. 

The feeling of pure jealousy towards a person you hadn’t even met before? It was burning hot, an intense pit of rage that churned your insides as well as shocked you. Why would you be jealous of your brother’s girlfriend? She wasn’t even rude, Reo had good taste. Truthfully, the poor girl did nothing bad. That didn’t stop you from showing your obvious disapproval though.

When she’d left, Reo had came up to you perplexed and slightly distraught like a lost puppy without his master.

“Hey sis? Did you not like her?”

“I don’t know… the way she sticks to you like a fly- I just don’t think she gives off great vibes you know? Tons of people go after you for money.”

“What if she’s different?”

“Didn’t seem different to me.”

And, unbeknownst to you, he had broken up with her the following day. Reo unconsciously cared about what you said to an inhumane extent. The day you said you wanted a chocolate on a whim he came back from a shopping trip with 5 boxes of fancy chocolates from Belgium along with a paper guide on growing your own cacao. As if he was capable of growing as much as a grass patch without it dying.

Knowing of your new unsoundly jealousy, Reo didn’t bring girls home anymore. He did, however, bring the Seishiro boy a lot. You didn’t mind, he was pretty sweet and didn’t do much apart from play with Reo on the PS5. Personally, you didn’t know what Reo saw in him apart from the looks, but you’d heard him praise his football skills so many times it was practically engraved in your memory.

It did, in fact, surprise you when Nagi talked to you for the first time. He’d popped up on your front door unannounced at 4PM on a Sunday with a flower. 

“It’s from Reo.”

“I- what?”

“The flower. It’s from Reo.”

“Thank you, but why?”

“He said he couldn’t be home tonight so he’s sorry.”

“Oh. Is he with that Yuki girl again?”

“Yeah.”

His lack of interest in this conversation was starting to get on your nerves. Could this guy put effort in something just once in his life?

“Hmph. I don’t like her.”

“Oh. Me too.”

“Really?”

“Yeah. She uses him for money.”

“…Don’t you?”

“Yeah, but I love him more than her.”

You sighed. Of course it was the money. But wait-

“You love him?”

“Forget I said that. You’re gonna get jealous.”

“What do you mean?”

You were genuinely confused now. Why would you be jealous of him?”

“You’re jealous of everyone Reo hangs out with. It’s painfully obvious really.”

That- that little piece of shit-

“That’s not true. I just want what’s best for him. And I’ve never been jealous of you, nor do I have a reason to be.”

“Hmm, if you say so. Well, here’s the flower. Just so you know, don’t be too harsh on his girlfriends. Every time you show one sign you don’t like them, he breaks up with them. I don’t really care, but it’s a hassle remembering all the names.”

Damn. That had to be the longest sentence you’d ever heard him say.

“Really? I never asked him to break up-”

“Yeah, well he did. How long’s Yuki gonna last? A day?”

“It’s not a game. It’s my brother’s love life!”

“I’m his best friend, I would know.”

“Fair enough.”

Really, what did Reo see in this guy?

“I don’t like Yuki.”

“You mentioned.”

“No, I was supposed to come over tonight, but she invited him to her house instead.”

“Oh, you were? You can stay if you want.”

“D’you have food?”

“There’s instant ramen in the kitchen.”

“Do you play?”

“Yeah, I beat Reo all the time!”

“Nice, can we play?”

“Sure, I don’t have anything today.”

And that’s how Reo had come back at 1AM to find the two of you eating an unhealthy amount of candy and instant ramen while playing Tetris on the play station.

A/N: for those who don’t know, yes that is a thing- you can play tetris on a PS

Since then, you’d talk to Nagi more often when he was around and usually let him stay whenever he needed a place to bunk at.

“Y/N, he’s my best friend, I notice.”

“Notice what??”

Reo had just gone to get chips as you were going to watch a movie.

“The way you stare at him.”

“Are you inferring I’m hitting on my own brother?”

“I’m not inferring.”

“You-”

God, you wanted to kill this boy.

“It’s obvious. He stares at you to. What kind of siblings even are you?”

“We’re step-siblings, thank you very much. This conversation is over.”

“If you say so.”

The evening had gone on without interruption, but the movie was relatively slow paced and you’d fallen asleep on your brother’s shoulder, mouth slightly open as you slept.

“Say Reo, I’m going to the bathroom okay?”

“Sure Sei I’ll just bring my sister back to her room.”

“You guys don’t share a room?”

“No.”

“You should.”

And with that, Sei stood up and left for the bathroom, leaving Reo to contemplate his thoughts as he picked you up bridal style in his arms. God you were so pretty like that. The little beads of sweat glistening on your forehead, your hair falling down your shoulders, it did things to him. Yes, you weren’t related… but it was still wrong. Oh, fuck it. Since Sei was obviously insinuating something, might as well act on it. Slightly ashamed but not regretful, Reo bent down and kissed your lips, lightly biting it.

Suddenly, he felt you stirring in his arms. He backed away fast, afraid at how you would react. Still tired, you managed to ask:

“Reo… were you kissing me?”

“I can explain-”

“Don’t.”

And with that, you grabbed his head and kissed him, hard. It was so fucking wrong, but it just felt right. His lips on yours, him holding you… you could melt right there. Shocked at your actions, Reo took some time to get his act together, but when he did, he kissed you back with a force that made you tremble. There was a passion that shouldn’t exist in this kiss, something long-awaited that shouldn’t have been fated, but was. The two of you meeting wasn’t fate, sure, but you’d made it to be, and that created meaning. You didn’t know why you felt like this, it was just a kiss- but it was a kiss you could only have dreamt of till now. A kiss that couldn’t be possible in this universe, a kiss that wasn’t meant to be. And yet, when your tongues intertwined like two malicious entities with no other thought but to devour, you knew you hadn’t fucked up.

The two of you parted, panting.

“I’ve never been kissed like that.”, you said, smiling.

“Me neither. None of my exes can do- that.”

“Reo, it’s common courtesy not to talk about your exes after kissing a girl.”

“Okay sis.”, he smirked.

“Feels wrong, doesn’t it?”, you mentioned.

“Does it? Feels really good to me.”

“No shame in kissing your sister while she sleeps huh?”

“…Not really. Is that bad?”

“Should be- but I liked it.”

“We’re both fucked up, aren’t we.”

“Yep. Now kiss me again.”

“Don’t have to tell me twice.”

And with that you were pinned on the couch, unable to breathe again. Unknown to the two of you, Nagi walked in.

“Get a room.”

“I- Sei, fuck- sorry- fuck- umm, it’s not what it looks liked.”, started a panicked Reo.

“Get a room? I’m sorry, aren’t you in our house?”

“I know, but show some decency. Also Reo, it’s definitely what it looks like.”

“Sei- I can explain!”

“Explain what? It’s painfully obvious since the start.”

“Is it?”

“Mhm.”, he nodded.

“Are you two going to continue?

“I- Sei, of course not!”

“Why not? Reo, you’re so bad at reading social cues I could die.”

“What do you mean Y/N?”

“He’s only asking because he wants to join. Is that it, Sei?”

“Yeah. Didn’t imagine you’d be the dominant one though.”

“Sexist idiot. Come here. The two of you have history, right?”

“Y/N, how do you know?” asked Reo.

“You’re my brother.”

“I told her.”

Both of your simultaneous answers contributed to a look of utter shock on Reo’s face that was enough to make you break a laugh. He only let out this side with you- even Sei was new to this. Sei? Wasn’t it Nagi- fuck it. He was going to join in, wasn’t he? Who the fuck would you be to sleep with a boy you weren’t on first-name basis with?

Chapter Text

“You- you told her?”

“You’re her brother, no?”

“I never realized the two of you got so close.”

“We’re not.”, Sei shook his head.

“Then why do you wan’t to join in?”

“I don’t know.”

“I- fair enough. Sis- fuck, that feels wrong. Y/N, are you okay with this?”

“No issue whatsoever.”

“Damn, okay. Where do you want to start?”

“Can you lay down for me?”

Sei whistled and went over to the couch and laid down.

“I was talking to Reo.”

“And? What if I want to lay down as well?”

“Oh- so- wait- Reo’s a top?”

“You didn’t know? Though apparently he bottoms with his sister, the horny shit.”

“Reo?”, you asked, raising an eyebrow.

“I don’t mind.”

“Okay then, then can I ride you?”

“I don’t see a problem with that.”

Reo grinned while he laid down and crossed his arms behind his head, hair down.

“Ah- Sei? What’d you want to do?”

“Finger you.”

“Direct! I like that! But- if I’m riding Reo, then how-? OH. You want to finger me there?”

Sei nodded, unfazed.

“Right. It’s normal to you. Well, I’ve never tried anal, so be nice. Oh, and there’s lube in second drawer of the side table. Right Reo?”

“How’d you know?”

“Once again, you and Sei aren't subtle! Now get the lube please Sei? You’re not touching my ass without prep.”

“Yes ma’am.”

“Don’t call me that, you’ll make me feel old! You’re older than me too…”

“…Okay.”

“Sorry about that sis, Sei has an age kink.”

“How the fuck do you know?”

“…”

“Never mind that… sorry Sei, it just makes me uncomfortable.”

“I get it. It’s not for everyone. Though you’re one to talk, about to ride your brother.”

“I guess you’re right. You can call me ma’am- but not all the time, okay baby?”

“…Thank you. That felt nice.”

“Kinky motherfucker. That’s my sister you’re talking to.”, teased Reo.

“Says the one spreading his legs for her.”

Sei glares at Reo lightly before going to get the lube. He came up to you and gently took off your jacket first.

“Can I undress you?”

“Go ahead, let’s give Reo a show.”, you smirked.

His hands started roaming your figure slowly, careful not to hurt you. He took of your shirt slowly and passed it over your head before unclipping your bra.

“How- how did you do it that fast?”

“It’s easy.”

“IT’S NOT EASY! I STRUGGLE EVERY EVENING!”

“Well now you can just call me and Reo to do it for you no?”

“I- that was fucking hot.”

“Glad to know.”

He continued by pulling off your pants and underwear down your legs, caressing them as he did so to make you shiver.

“Am I doing okay ma’am?”

You shake a little before praising him.

“Yes baby you’re doing fine. Just a little cold.”

“I’ll warm you up just fine.” added Reo, grinning.

Sei smiled at his given nickname and continued caressing your now naked body in front of Reo.

“…Stop being handsy like that with my sister Seishiro.”

“You’re about to shove your dick in her, shut up.”

“It’s fine Reo, I like it.”

“I know you do but I wish it was me.”

Sei harrumphed before letting his hands rest on your waist and lowering you down on Reo’s penis with a soft ‘plop’.

“Fuck… sis- why’d you have to squeeze me so fucking good…”, groaned Reo blissfully.

You let out a slight gasp as he filled up your insides, his large girth spreading your walls so sweetly as you moaned softly. This was so goddamn wrong and it only made it feel better, your walls sucking the one you called your brother in so greedily it was ironic. Suddenly, you emitted a low whine at the feeling of a cold liquid in your lower region.

“Is- this fine?”, asked Sei.

“Y- yeah- sure.”

He slowly entered one lubed up finger into your ass while you started riding Reo, bouncing up and down on his cock.

“Sis- so warm… ungh-”, grunted Reo as you fucked yourself silly on him.

“Ah- ah… Sei yeah that’s good- keep going baby- UNGH REO-”, you yelled as you inadvertently found your sweet spot.

You aggressively let yourself fall down onto the same spot repeatedly, pounding your insides as Reo moaned lightly under you, happy to be ridden like this by his step-sister like the disturbed man he was, fully enjoying this.

“Hmm- Reo- gonna cum…”

“Okay the, cum for me sis alright? Cum on your brother’s dick?”

The mere thought of that sentence sent you into shambles as you came hard, your orgasm making your vision hazy as you fell onto Reo’s chest, Sei’s fingers still up your ass.

“The two of you are so lewd. I like it.”, noted Sei from behind you, his slender digits still pumping inside your ass sending your brain into overload.

“Come on sis, I know you have more in you? Here, I need to come as well, no? What about Sei?”, teased Reo gently, pulling you off him before sitting up.

“Here sis, I’ll fuck you again while Sei takes your ass that he so nicely prepped, right baby, you did a good job?”

Sei nodded happily while you whined some sort of approval as you tried to sit up and failed.

“Fucked yourself dumb on my cock, didn’t you sis? So lewd. Can’t say I didn’t love seeing you above me though. You’ll bottom this time… gotta make you cum again.”

Reo positioned himself and slid into you harshly before Sei entered you from the back, stretching you out little by little. It burnt a little, but it soon felt pleasurable as well when he bottomed out. The two started moving in sync, pounding into you mercilessly, pushed on by the heavy moans you let out. Tears threatened your eyes from the overstimulation as you reached your second orgasm, vision blanking out. Your juices coated your brother’s cock as your ass clenched around Sei, pulling him in further while he groaned lightly.

“Fuck- did she black out?”

“It’s okay if we continue Reo, right?”

“Yeah. Not too harsh.”

“Of course.”

The two boys kept thrusting into you, reaching their climax. Sei pulled out and came on your back, the streaks of semen coating your skin giving it an opalescent shine to go along with the sweat beads pearling up. Reo thrust in one last time before coming deep inside you, the thick liquid filling you up warmly as you woke up.

“Reo- you didn’t use a condom… it’s your sister.”

“Fuck- Sei- I’ll buy her the morning after pill. I don’t even know if she’s on birth control… shit, I should’ve asked… but she’d look so pretty, all round and carrying my baby.”

“And you call me a kinky motherfucker for calling her ma’am… you’re talking about breeding your sister!”

“…We’re not technically related.”

“You’re sick.”

“You love it.”, Reo chuckled.

You woke up to a few lazy thrusts from Reo as he pumped his cum deeper inside you on instinct.

“Huh- ahhhh- too much….”

“You blacked out sis, but it’s okay now. I’ll let you rest and fuck Sei while you do that, okay? We’ll take care of you more, don’t worry.”

And with that, Reo grabbed Sei by the neck and turned him so that he was on his knees, head lodged into the couch. Sei moaned at the intense contact and let out a high-pitched whine as Reo filled him, his walls sucking him in greedily.

“That’s a good boy… taking me in so well withno prep- god you really were meant to take dick weren’t you baby?”

Sei let out a small moan as an agreement as Reo thrusted roughly into him, pushing Sei’s head into the couch as he moaned of pleasure. Reo placed his hand on Sei’s neck, squeezing slightly as Sei gasped.

“If I remember correctly, you like being choked, right baby?”

“…Yes…”

“Good boy.”

Reo started squeezing tighter as Sei let out a high moan from the intense dose of adrenaline it was giving him, the skin of his neck red and scorched as he whined.

“Ungh- ah- taking me great, aren’t you baby?”

“Yes- yes- ahhh, right there daddy…”

“Daddy? That’s a first. Well then, will you take daddy’s load?”, asks Reo, inquisitively.

“Mhm- I’ll be a good boy- ungh- right there…”

Sei came untouched, spurting out cum over his chest with some getting onto his face like a pornstar while Reo came inside him, hand still gripping Sei’s neck.

“Did so well for me baby. Let’s help my sis out now, okay?”

Pulling out of Sei swiftly, he came over to you as you lay there, spent, and laid a small kiss on your forehead.

“I filled you up so well, sis… you look so cute with my cum flowing out of you. I’ma lick it all up, okay?”

Reo lowered his head down between your thighs while Sei played absent-mindedly with your hair and started licking up your mixed juices, sucking on your clit as he did so causing you to let out a shocked moan. His tongue was devilishly slurping up the liquids inside your cunt as you moaned, unaware oral could feel so good. You reached a third orgasm as you squirted on Reo’s face.

“Aww sis, giving me more to drink, so generous.”

And with that, he sat up and kissed you. You could taste yourself on his mouth and you didn’t mind, sinking in to the warm feeling of the kiss, unable to grasp how wrong this situation was as you fell into the smooth feeling of his lips. Sei kept playing with your hair, his slender fingers untangling your locks carefully.

“Thank you.”, you said.

“Both of you.”

Sei nodded gently and Reo hugged you.

“I never knew I’d get to fuck my sister?”

“I did.”, said Sei, unfazed.

“…ha, you did.”, chuckled Reo.

“You’ll get to do it again.”, you assured him, still panting.

“What about me?”, asked Sei.

“What do you think?”

“Well then, you’ll see a lot of me.”

“Looking forward to it.”, you grinned.