Posted originally on the Archive_of_Our_Own at https://archiveofourown.org/
works/10078379.
  Rating:
      Explicit
  Archive Warning:
      Underage
  Category:
      M/M
  Fandom:
      Kuroko_no_Basuke_|_Kuroko's_Basketball
  Relationship:
      Akashi_Seijuurou/Kuroko_Tetsuya
  Additional Tags:
      Smut, Light_Angst, Sibling_Incest, between_twins, haaaah_this_is_the_most
      disgusting_thing_i've_ever_written, Akashi_and_Kuroko_are_twins, yup._see
      you_all_in_hell., Canon_Compliant, set_during_the_winter_cup
  Stats:
      Published: 2017-03-04 Words: 3585
****** Sweetest Sin ******
by herdustisverypretty
Summary
     ‘The forbidden fruit is the sweetest.’ Seijuurou knows this all too
     well. For the fruit he desires is not just his blood but his brother,
     his twin, his mirror image, his soulmate in every possible way. And
     Tetsuya is so very sweet.
Notes
     Well. Here we are. When I found out they were originally going to be
     siblings... This was inevitable. I made them twins so they're still
     in the same year. Fraternal, obviously.
     Been working on this for a while, but I only finished it today (this
     morning? it's 2am and I'm writing this monstrosity)
     Kuroko became really shoujo. Shy and delicate and cute. Forgive me.
     Not beta'd because I'm too embarrassed to send this awful thing to
     anyone. Weehoo.
     An exasperated reminder: There is a difference between fiction and
     reality. If you can't tell the difference, you really should stay far
     away from this story and keep your opinions to yourself. Thank.
See the end of the work for more notes
‘The forbidden fruit is the sweetest.’
Seijuurou knows this all too well. For the fruit he desires is not just his
blood but his brother, his twin, his mirror image, his soulmate in every
possible way. And Tetsuya is so very sweet.
He’s in Tokyo at the moment, for the Winter Cup. He saw Seirin’s game against
Yousen, saw Tetsuya win, how he saved their team at the end. Seijuurou is
pleased to see Tetsuya happy. He hopes to see him reach the finals.
He leaves his hotel room, not wanting to be cooped up in it anymore. He wants
to see Tetsuya. He pulls his phone out of his pocket and presses Tetsuya’s name
in his contacts.
“Hello?” the sweet, sweet voice answers. Honestly, he’s almost surprised his
twin picked up at all. He half expected him not to answer when he saw
Seijuurou’s name on his screen.
“Tetsuya,” Seijuurou says.
“Nii-san, why are you calling me?”
“Where you are at the moment?”
Tetsuya pauses. “I’m with my teammates. We’re at the Maji Burger near our
school.” He was always weak to Seijuurou, always easily giving in to him.
“Excellent. Stay there, I’ll be there soon.”
“Nii-”
He ends the call and climbs into the car already waiting for him. He hopes
Tetsuya obeys and doesn’t wander off. He’s not been doing what Seijuurou wants
lately. Thankfully when he arrives, Tetsuya is inside. Unfortunately though,
he’s sitting with Kagami. At least the other Seirin members aren’t there
anymore.
“Nii-san,” Tetsuya says when he sees him. “Why did you want to come?”
“Yeah, what are you up to?” Kagami asks with narrowed eyes.
Seijuurou holds off a sigh. “Nothing that concerns you. I wanted to see my
brother. Is that such an offense to you?” Kagami snorts. Seijuurou sits down
next to Tetsuya, and looks over at the taller redhead. “Do you mind giving us
some privacy?”
Kagami stares at him for a moment, then looks at Tetsuya. “Kuroko, you okay?”
he asks him.
Their surnames have always been curious. Despite their parents being married,
their mother wanted to keep her surname, so when the twins had been born,
Seijuurou, the older twin, took their father’s name, while Tetsuya, the younger
twin, took their mother’s name. Throughout their lives, often people didn’t
even realise they were related at all. They’re not identical twins, and with
their different hair and eye colours, it’s easy to mistake them as just friends
and not brothers.
“Yes, I am fine, Kagami-kun. Please wait for me.”
Kagami nods and then leaves, giving Seijuurou a slight glare as he walks off.
“My, he’s a bit wild, isn’t he?” Seijuurou says.
“What are you doing here?”
“I already said. I wanted to see you. I saw your game today.”
Tetsuya is staring at his hands now. “Oh. What did you think?”
“You did well. I’m impressed.”
“Thank you…”
“I’m looking forward to seeing you play against Ryouta. I’m sure it will be
interesting.”
“I’ve been practicing hard. I hope we win.”
Seijuurou smiles. “Good. I want to see if we can battle each other at the end.”
He wants to reach out and play with the lock of hair sitting over Tetsuya’s
ear. His hair has always been soft and silky, and it always smells like
vanilla.
Tetsuya still doesn’t look at him. “Do you want to win against me?”
“Not necessarily. If you won that would be interesting. I would be upset that I
lost but I would be happy that you won,” Seijuurou explains. He smiles. “But I
won’t lose.”
“We’ll see,” Tetsuya says softly.
“Tetsuya, will you look at me?” Seijuurou asks. He has to be careful with his
twin. He’s like a cornered animal. One wrong move and he’ll bring up walls
around himself, not allowing anyone in, even Seijuurou. It wasn’t always like
that. Once, Seijuurou was the most important person to Tetsuya. But things have
changed.
“We haven’t talked in months. Why are you so interested in me now?”
Part-way through their third year of middle school, Tetsuya decided he was
going to move in with their grandmother. She’s old, but she manages fine,
though Tetsuya insisted on taking care of her. That was his reason, though
Seijuurou knows Tetsuya was running away from him.
He contemplates his answer. He can’t exactly say the reason he never contacted
Tetsuya this past year is because he almost can’t control himself around him.
And also because he was so furious at Tetsuya for leaving that he might have
done something to him that he would regret. Towards the end of Teikou, his
small and vulnerable twin was almost impossible to resist. And Seijuurou may be
an utter sadist, but he doesn’t want to destroy Tetsuya. “Maybe I was upset at
you for abandoning me.”
“I had good reason.”
Seijuurou’s brows twitch. “I see. But I want to talk to you now. Will you
accept me?”
Tetsuya finally glances at him. He looks unsure. “I can do that. For you.”
Seijuurou smiles. “Good.” He looks up to where Kagami is leaning on the wall at
the other end of the restaurant and glaring at them. “I suppose I should leave
you to your friend.”
“I would appreciate that.”
“May I request an embrace before I go?”
He can be hopeful at least.
Tetsuya actually smiles a little, an almost amused look. “Go ahead.”
Seijuurou leans in and wraps his arms gently around him. He’s so small and
delicate, that hasn’t changed. Tetsuya hugs him back, and Seijuurou sighs
softly. He’s missed touching his twin. He’s missed being close to him. He’s
missed smelling him and holding him. He finally tears himself away, aware that
their hug has gone on for too long to be normal. He places a light kiss on
Tetsuya’s cheek before pulling back. It’s something he did when they were
younger. It used to calm Tetsuya’s anxiety.
“I’ll see you soon,” Seijuurou says. “Keep in touch.”
Tetsuya just nods, not looking at him again.
===============================================================================
 
“Ah- Aah! Nii-san!”
Seijuurou is living out his dream. He has Tetsuya pinned under him, naked and
covered in a delicious sweat. His legs are wide open and hooked around
Seijuurou’s hips as Seijuurou fucks him. Tetsuya’s body is so tight and
scorching hot, sucking Seijuurou in further as he moans and cries wantonly.
He’s dripping onto his stomach, but Seijuurou refuses to touch him just yet. He
wants to torture his twin. And it’s working. There are tears in Tetsuya’s eyes
and spilling down the side of his face, and he’s making little choked sobbing
noises. Seijuurou can tell he’s in pain, but he knows Tetsuya is also enjoying
it immensely. He grips Tetsuya’s hips tighter, hoping to leave bruises, and he
thrusts in deep again. He slides against Tetsuya’s sweet spot every time, and
his twin sobs loudly.
“Nii-san, Nii-san, aaah!” he cries, his back arching off the bed.
“Are you going to come, Tetsuya?” Seijuurou asks him in his steadiest voice.
Tetsuya nods, making a little choked noise again. “Please, please touch me,
Nii-san,” he begs.
Seijuurou kisses him, a messy, open-mouthed kiss. “As you wish, my love.”
He wraps his hand around Tetsuya’s cock, and his twin screams. Seijuurou only
needs to stroke him a few times before he’s crying out and his come is
splattering between them. Tetsuya’s gone limp, lying against the mattress in
exhaustion, but after a moment he starts to roll his hips with Seijuurou’s
thrusts, and the older twin moans, digging his nails into Tetsuya’s hips as he
comes and fills up Tetsuya’s insides with warmth. Seijuurou drops onto his
love, and Tetsuya wraps his arms around him in a gentle embrace. They’re both
panting, desperate for air.
“Nii-san, it feels gross,” Tetsuya mumbles.
Seijuurou smiles and kisses his forehead. He slides out, relishing in the lewd
squelch that follows, and he stares in awed delight at the sight of his come
dripping out of Tetsuya’s abused body.
“Don’t look,” Tetsuya says, snapping his legs shut.
Seijuurou grins and pushes Tetsuya’s knees open again, and he rubs the pad of
his middle finger over Tetsuya’s stretched and sticky hole. His twin gasps and
whines, squirming uncomfortably from oversensitivity.
“I want to go again,” Seijuurou murmurs.
Tetsuya blushes. “We’ve already done it twice…”
“It’s not enough. I need more of you,” Seijuurou says, nuzzling against
Tetsuya’s neck.
“You’re gross.”
Seijuurou grins. “You’re equally as filthy.”
Tetsuya blushes deeper and doesn’t say anything. They snuggle against each
other, and Seijuurou slides his hands down Tetsuya’s back to rest on his ass,
squeezing it gently. Tetsuya makes a little whimper.
“Are you in pain?” Seijuurou asks softly.
“It’s okay. I’m happy. I love you, Nii-san,” Tetsuya murmurs.
Seijuurou leans in to kiss him, but he just finds air. He opens his eyes to see
that Tetsuya is gone. And that’s when he wakes up. He sits up, rubbing his
eyes. He feels stickiness in his pants and he scowls. It had been such a good
dream too.
===============================================================================
 
Seijuurou is sitting in his room. The school year has ended, and so he’s come
home to the Akashi mansion in Tokyo. He sometimes comes home on weekends, but
mostly he stays at Rakuzan to study, but it’s not as if Tetsuya has been at
home waiting for him anyway.
He sits down on the bed. They always shared a bed. Tetsuya insisted on it as a
child. Even when they grew into teenagers, he still wanted to share. They never
fought, and Tetsuya was always happy to snuggle up against Seijuurou as they
slept. Until the change at Teikou –  Seijuurou’s personality shift. He was
quite content to let his second self remain in control, as long as they
continued to win. His second self was always respectful to Tetsuya as well, so
that wasn’t a concern; even he was in love with their twin. The real Seijuurou
can’t blame him. Tetsuya is perfect in their eyes. But the real him had to come
back.
“Nii-san, are you ready for bed?”
Seijuurou looks up at Tetsuya and smiles. “Yes, have you brushed your teeth?”
Tetsuya nods. He’s dressed in a plain white T-shirt paired with pyjama bottoms
the same shade as his hair and printed with turtles. Seijuurou almost wants to
scream at how adorable his twin is. Tetsuya has always liked cute things like
that. Seijuurou likes cute things like Tetsuya.
“Then I’ll go see to mine. Get into bed, I’ll be back in a minute.”
Tetsuya hesitates, twisting his hands. “Nii-san…”
“Yes? What is it?”
He shakes his head. “Nothing. I’ll be here when you get back.”
Seijuurou smiles. “I should hope so. I don’t want you running away again.”
Tetsuya offers him a small smile. “I’m not going anywhere.”
 Seijuurou returns the smile then heads into their en suite bathroom to finish
getting ready for the night. When he comes back out to the room, Tetsuya is
tucked into bed and sleeping already. Seijuurou smiles and walks gently over to
join him.
“It’s good to have you back,” he murmurs, brushing some of Tetsuya’s fringe off
his forehead. He reaches over and flicks off the bedside lamp, then scoots down
to get comfortable. Within a moment of his back touching the mattress, Tetsuya
is suddenly pressing against him, arms scooping around his body.
“Nii-san…” he says quietly.
“You were awake?” Seijuurou asks.
“Mm. It’s good to have you back too. The you I love.”
“You don’t love the other half of me?” Seijuurou jokingly asks.
“He’s okay. But I prefer you like this. You’re happier.”
Seijuurou smiles and turns over, pulling Tetsuya even closer against himself.
“I’m glad I get to be with you properly again. I’m also glad you forgave me.”
“Of course I did…” Tetsuya nuzzles into Seijuurou’s neck. The older twin’s
heart is beating a little faster than he might have liked. “Nii-san… I-”
“It’s okay, I’m here, Tetsuya.”
Tetsuya buries closer, and Seijuurou can feel wet warmth dripping onto his
collarbone. He doesn’t say anything more, just rubs comforting circles into his
brother’s back until the both of them fall asleep.
===============================================================================
 
Seijuurou wakes up early. He’s used to it, but Tetsuya tends to sleep in, so
Seijuurou sits up carefully so as not to disturb him. Tetsuya hasn’t had as
hard a life as Seijuurou, even after their mother died, Tetsuya got off
lightly. He didn’t have nearly as much work, and wasn’t scolded as harshly.
He’s the innocent baby of the family. He’s the smaller, weaker twin. He’s not
the heir. Seijuurou has never felt any sort of resentment though, in fact he
only has ever wanted to keep things that way, to protect his younger brother
from the harshness of this family. Truth be told he was a little glad when
Tetsuya moved out to live with their grandmother, because he knew she’d be much
kinder than if Tetsuya was living alone with their father.
He gets up and decides to get ready for the day; it’s engrained in his mind to
have his regular routine, even during the holidays. He’s in the bathroom about
to step into the shower when he hears the door creak open.
“Tetsuya, you’re awake,” he says, turning around.
Tetsuya is avoiding his gaze, staring at the floor instead. His hair is a mess,
as per usual. Seijuurou has missed seeing that ridiculous bed hair.
“I was wondering if we could get ready together?”
Seijuurou blinks at him a few times. “Of course. It’s been a while since we did
this, hasn’t it?”
Tetsuya nods quietly, then starts to pull off his clothes. Seijuurou wonders if
perhaps people would think this weird, how intimate they are. They always
bathed together as children, and like the sharing of a bed, they still
sometimes showered when older as well. Tetsuya says it’s to save water, though
Seijuurou is quite positive that he does enjoy being close to his twin.
Seijuurou feels a little disappointed that it’s probably only platonic.
He really is disgusting.
They step into the shower, and Tetsuya timidly comes closer.
“Want me to wash your hair?” Seijuurou asks with a smile.
“If you’d like.”
So that’s a yes. Seijuurou is good at reading his twin. They always use their
own separate shampoos and conditioners, Tetsuya likes vanilla while Seijuurou
uses cherry blossom. Seijuurou tips some of Tetsuya’s signature shampoo into
his palm and then starts to work it into his pastel blue hair. Tetsuya leans
back into his touch, and his tense shoulders relax. Seijuurou can’t help but
sneak a glance down Tetsuya’s body, and he gulps at the sight of the water
dripping down his smooth skin.
“Nii-san?”
Seijuurou snaps his eyes upwards and focuses on massaging Tetsuya’s scalp
again. “Sorry, I was- thinking about things.”
“Oh? What were you thinking of?”
“Mm, nothing important.”
“It must have been important if it distracted you.”
Seijuurou pauses, biting his lip. He could just so easily run his hands down
Tetsuya’s body, push him against the shower wall and take him right then and
there. But he can’t.
“You wouldn’t like it if I told you,” he says at last.
“What is it? You can tell me. We tell each other everything.”
“Rinse your hair,” Seijuurou instructs softly.
Tetsuya does, stepping under the water and cleaning off the lathered bubbles.
He takes Seijuurou’s wrist in his delicate fingers when he’s done.
“Please tell me, Nii-san.”
Seijuurou stares at him, with his big, innocent doe eyes, begging for the
truth.
“Promise me you won’t run away again?”
Tetsuya smiles reassuringly. “I promise.”
Seijuurou touches his shoulders, gently guiding Tetsuya to press against the
wall, and then he kisses him. Tetsuya doesn’t respond at first, and Seijuurou
thinks with a sinking heart that he must just be in such a shock that he
doesn’t know what to do. He’s expecting to be pushed away, but is surprised
when Tetsuya’s hands move to his back to tug him closer. Their bodies press
together, skin sliding as they move and sending sparks through Seijuurou’s
bones. Tetsuya opens his mouth, and Seijuurou eagerly slips his tongue inside,
swirling and pressing against Tetsuya’s hungrily, as if he’ll never get to do
this again. He gasps in surprise when he feels Tetsuya growing hard against
him.
“Aah- Nii-san,” Tetsuya squeaks, pushing him back. Seijuurou isn’t sure if it’s
the heat from the water or embarrassment, or both, but Tetsuya’s face is
flushed bright red. “Uh, I’m so embarrassed.”
Seijuurou actually laughs. “Please don’t be. There’s no need with me.”
“But I- um… this,” Tetsuya says, gesturing to his lower half.
Seijuurou grins wickedly. “Will you let me take care of you?”
Tetsuya’s eyes widen, and he seems to blush even harder. “If-If you wish.”
Another yes.
Seijuurou turns the water off and lifts his twin into his arms, Tetsuya’s legs
hooking around his hips.
“Aah! Nii-san, don’t pick me up like that!”
“Just relax,” Seijuurou says with a smile.
He carries Tetsuya out of the bathroom and lays him down on their bed, climbing
over him. They’re still dripping. Seijuurou kisses Tetsuya again, another open-
mouthed kiss, his tongue mapping out Tetsuya’s, committing his taste to memory.
He pushes Tetsuya’s legs open around him, settling between his thighs. Tetsuya
holds his arms to his chest protectively, clearly embarrassed, so Seijuurou
kisses his sweet lips to help calm him a little.
“Please tell me if you want me to stop,” he says.
“I wouldn’t want you to. You can have me in every way and I’d never want it to
stop.”
Seijuurou’s heart feels like it’s bursting out of his chest. He presses their
lips together, kissing Tetsuya with more intensity than before. His twin moans
into his mouth, and Seijuurou could get drunk off those sounds. He starts to
move his hands along Tetsuya’s damp body, feeling the curve of his waist, his
bony hips, and finally his already leaking cock. Tetsuya squeaks in response at
the touch, his thighs squeezing Seijuurou’s hips lightly. Seijuurou pulls back
so he can watch Tetsuya’s expressions, and he’s not disappointed. Tetsuya’s
eyes are closed, his pretty, pink lips formed in an ‘O’ shape, gasping and
whimpering softly.
“You’re so beautiful,” Seijuurou murmurs.
“Aaah- nnh, no, not like you,” Tetsuya gasps out.
Seijuurou smiles. “Shh. Relax.”
He gently strokes along Tetsuya’s hardened skin, making him moan and whine
beautifully. He can feel Tetsuya’s release coming, can feel the tension in his
body building as his noises grow louder and his harsh breathing quickens.
Tetsuya comes with a sweet moan, warmth spilling over Seijuurou’s hand and onto
his stomach. His breathing is still rapid, and his face is flushed, his eyes
avoiding Seijuurou. The older twin raises his sticky hand to lick up a bit of
the fluid, smiling when Tetsuya makes a little squeak in shock. The taste is
salty and bitter, but Seijuurou doesn’t mind it, it’s Tetsuya’s after all.
“Nii-san,” Tetsuya says in a choked voice.
Seijuurou is instantly concerned. “Are you okay? Was that too much? Have I gone
too far?”
“No, no, that’s not it.” Tetsuya sits up and pushes Seijuurou back against the
headboard.
He eyes down his brother’s figure, gentle hands roaming across Seijuurou’s body
curiously, inching lower until they’re both wrapped around Seijuurou’s cock.
The older twin moans softly, his fingers squeezing into the sheets beneath him
tightly. Tetsuya moves his hands a little faster, until Seijuurou is panting
and sweat is dripping down his face. Tetsuya pushes Seijuurou to lie down more,
and he bends down, his backside raised in the air a little as he licks at
Seijuurou’s cock experimentally. Seijuurou instantly lets him know how he
feels, moaning and grasping at pastel hair. Seeming more confident, Tetsuya
swallows him whole, and he chokes a little, but he perseveres, sinking down and
back up, down and back up. He’s bobbing quickly, his cherry lips stretched
tight and his cheeks hollowed, and Seijuurou can see tears gathering in his
eyes. He should tell Tetsuya to stop, that he doesn’t have to do this, but it
feels too good, it’s everything Seijuurou’s ever wanted come to life, that he
just lays back and lets his twin work.
“Tetsuya,” he says in a warning tone. “I’m going to come if you keep going.”
His twin pulls off with a deep gasp. “Then relax,” is all he says before he
drops back down and his warm mouth swallows Seijuurou again.
Seijuurou tugs on Tetsuya’s hair harshly when he comes, making a little groan
as he spills into Tetsuya’s mouth. The come dribbles down Tetsuya’s chin,
dripping onto the sheets as he struggles to swallow everything. He sits back
with damp eyelashes and looking thoroughly debauched, wiping off the mess with
his hand.
Seijuurou grabs him and pulls him so they’re pressed together again, kissing
him passionately. He can taste himself, but he doesn’t care, it’s kind of hot
even, thinking about what his twin just did for him.
“Tetsuya,” he says breathlessly, “I love you more than anything.”
His twin blushes. “I love you the same. I’m so thankful you feel the same way.”
Seijuurou smiles. “Me too.” He gently rubs Tetsuya’s waist. “We probably should
shower again.”
Tetsuya nods. “Only if we do it together.”
“Of course. We’ll be together forever. You’re my soulmate,” Seijuurou declares.
Tetsuya smiles shyly. “You’re embarrassing.”
Seijuurou hums happily. He strokes his fingertips down Tetsuya’s still blushing
cheek. “Come on, love, we need to clean up.”
End Notes
     My tactic for keeping their canon last names. How bout that. *finger
     guns* It's so awkward, pls punch me.
     Pls give me comments if you liked this. I would appreciate the
     feedback. Let us all join hands and appreciate this sin circle.
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