Title: Need
Pairing: Farroncest (Lightning/Serah)
Rating: M for sisterly incest, some language
Words: 4,054
Song Inspirations: "Galaxy In Janaki" - Flying Lotus, "Dust To Dust" - FXIII OST
Prompt Request: "Their first time. They know it's wrong, but they can't help themselves."

Disclaimer: I do not own the characters in this fic. They belong to their rightful owners.

A/N: Okay, so here's another product of my writer's block for "Bonding." I promise I will get the final chapter of that fic out, but I'm just having a bit of trouble right now, haha. Anyway. This fic was made to fill a very old prompt request on the first FFXIII Kink Meme. In a way, I guess this kind of serves as my own personal headcanon, or at least until I can write a better one. Enjoy!

Serah drums her fingers on her sister's mattress, her scrutinizing gaze fixed on Lightning's half-naked, athletic frame moving back and forth through the room.

It's late evening. Lightning had returned from work earlier than usual and the Farron sisters were able to enjoy dinner together, the first time in three weeks. Serah was ecstatic and made sure to prepare her sister's favorite meal. Afterwards, Lightning showered and Serah reminded herself to do something she'd been meaning to do for a while.

She'd asked Lightning to talk, just to talk, as they hadn't done so in forever. Corporal Lightning Farron was far too busy nowadays, too tied up in work. Serah was sure her sister didn't mean it, but it was hurting her.

With an exaggerated sigh, Lightning tugs on the t-shirt she's holding and flops down on the bed, her eyes closing. "What's up?"

"I just…wanted to talk, sis," Serah whispers.

Lightning rubs her hands through her hair then over her face. "I know. I know, Serah. I'm so sorry. I've just been busy and-"

"Light, it's okay. It's fine, really." She bites her lip. What a terrible lie that was; she's dying on the inside. Still, she believes her sister. Lightning does what's necessary for them to survive – making just enough money to get by – and Serah is thankful for it all. "Can we just talk? You know, like we used to?"

"Sure. Sure, Serah." Lightning smiles, surely a forced one, as she rises to sit up on the bed. "Come here, you."

"Oh- hey! Light!" Serah laughs. She feels arms wrap around her and pull her close. Before she knows it, she's flush against her sister's bosom. Her cheeks burn with an oncoming blush. She presses into Lightning's chest and relaxes when she feels a chin rest atop her head.

The elder Farron exhales softly. "So, what's on your mind?"

What…is on her mind exactly? "Umm, I dunno. I just- well, we haven't talked in so long." Serah curls up closer.

There's a short pause before Lightning answers. "Serah, I really am sorry. I've just been so busy with work and catching up on sleep."

Serah says nothing, just sighs as Lightning tightens the grip around her.

"Is everything okay at school? No one bothering you, right?"

Serah smiles a little. "No, not at all. Everything's fine. School's getting a bit hectic with testing coming up but nothing I can't manage."

"Good. I know you can do it. I'm so proud of you."

Serah's face heats up and she can't help but smile wider. "How's work? You know, besides being tiring and all."

Lightning shifts her legs. "Good so far. The Lieutenant says I'll be up for another promotion in a few months so when that comes, I'll be getting paid more."

"Already? Didn't you just get promoted not too long ago?"

The corporal chuckles. "Yeah, I did. I've been trying to work hard for you. Everything's so different now. Nothing…has been the same since-"

"I know, Light. Ever since…ever since Mom and Dad died." Serah's heart skips a beat at the words she speaks. She shuts her eyes. As harsh as it is, it's the solid truth.

Life changed for the Farrons after their parents passed away. Lightning grew up as fast she could, joining Guardian Corps. after high school in order to keep a roof over their heads. Serah helped out as much as possible after Lightning joined the military, hoping to take some of the stress off her older sister and guardian.

"It's been four years since Mom passed." Lightning presses her lips to Serah's hair. "And you probably don't even remember Dad, do you?"

"No." Of course she doesn't. Serah was only two. Lightning and her mother always told her he was a great man. That was the only memory she needed of him. But her mother? "Light?" Her throat constricts tight, nearly closes. With a hand, she fingers the bolt-shaped necklace around Lightning's neck. She encloses the other around one of her sister's arms and squeezes, then runs a thumb over one spot - a small, jagged scar from basic training, she recalls.

"Hmm?"

Fingers brush Serah's side over the fabric of her tanktop. She tucks her head further under Lightning's chin, biting her bottom lip and tasting the salt of tears that run down her cheek. "I- I miss Mom," she whispers through choked sobs. She's pulled closer into her sister's embrace.

Lightning rubs Serah's side. Her voice lowers, becomes thick. "I know. I know, Serah."

Serah's eyes begin to burn with oncoming tears. So intense, so sudden. It was needed. Over the course of four years, she never had time. She never had one chance to stop and truly mourn the loss of their parents. Late night crying into slumber was present, but it didn't have the same effect, not of this magnitude. It only takes a minute before she's full-out sobbing. Her cries wrack her small frame, uncontrollable, shaking Lightning and the bed with her.

"Shhh, shhh, it's okay. It's okay, Serah."

Lightning shifts just slightly, enough where Serah can relax further into her arms. The younger Farron moves her own arms, wrapping them around Lightning's midsection in a tight hug. The front of Lightning's shirt is soaked with her tears. She doesn't care. It's only when she senses something cold on her scalp that she sobs harder; Lightning, her guardian and protector, is crying.

"It's okay, Serah. I'm here, okay? I'm here," Lightning rasps. The soldier holds her sister tight in her arms, rocking back and forth.

It takes the better part of an hour before Serah slows her weeping. She opens her eyes to her sister's dark shirt. The thumping of a heartbeat and shallow breaths reach her ears. Her sister is unmoving, still alive, of course, but unmoving. She sighs.

"Serah."

Serah shakes at her name. She doesn't respond.

Lightning clears her throat. "Serah. I'm sorry."

What? She furrows her eyebrows.

The elder Farron releases Serah and looks her dead in the eye before she speaks. "I'm sorry. I-I can't be like Mom. I can't." She pauses.

Tilting her head to the side, Serah stares back. "Lightning?"

Lightning rests her forehead against Serah's, cupping the girl's cheek with one hand. "I can't be like Mom. I can't. But Serah, I promise I'll do whatever I can for you."

Silence. Serah doesn't utter a word, but the threat of fresh tears burns her eyes.

"You're my only family left and I don't want to lose you, too. Just- just know that I love you, Serah. More than anything in this world."

Serah does not move, only stares into her sister's eyes, sapphire holding an aquamarine gaze. She opens her mouth twice before words come out in a hushed whisper. "I love you, too, Lightning."

A sigh escapes Lightning and she shuts her eyes.

Serah remains there, motionless. For the longest time, the death of their parents had taken a horrible toll on their relationship. While it brought the two closer together emotionally, it also physically drove them apart. But now, the two have a chance to mourn with one another and something inside of Serah confuses her. She's happy – finally able to accept her parents' deaths and truly begin to move on; at the same time, something stirs inside of her, rears its ugly, disgusting head. She closes her eyes just briefly and really feels the palm on her cheek. As she rests there, she heats up. Had her sister's hand ever felt so…soft, so warm and comforting? She never paid any mind, not until now. Why now? Why does she pay so much attention to that, the warm, subtle breaths against her face, and larger, more athletic frame against her now? A blush creeps upon her face and neck and an unfamiliar burning seeps into her core.

Lightning opens her eyes. "Serah-"

And Serah presses her lips against Lightning. It's only a light brush, an off-centered not-so-innocent brush over lightly chapped lips. She doesn't care; something in her does not give a flan's ass until she realizes she's being pushed away by her shoulders.

"Serah!" Lightning growls, shaking her head. Her eyes are narrowed and feral blue. Her grip on Serah's shoulders loosens.

Wrong. That was wrong. So, so wrong. Serah's eyes dart everywhere; she doesn't know where to look. She lowers her head, hung low in shame. Why on Cocoon would she think about kissing her own sister? "Light- I- I'm sorry. I didn't- I wasn't thinking." She didn't know what she was thinking; it just happened.

Lightning's expression softens, but still retains the stern, scolding look of before. "No. Serah- I- no. It can't be like this." She tilts her head downwards for a few seconds. "I know, okay. I get what you're feeling. I understand, but-" Her voice lowers to a hiss. "We can't. We can't do this."

Serah knows this; she doesn't need to be told. Having any kind of feelings for your own sibling – romantic, sexual, or otherwise – was wrong. It was…sinful. But were they even feelings or just an aching need? She raises her head to look at her older sister. Serah locks eyes with Lightning. In an instant, she throws those thoughts away. Why should she care? No one had to know. "Lightning, please? I need you." She mimics Lightning from before, resting her own head against hers and placing a small hand on Lightning's cheek. She leans in again for another kiss.

Lightning remains frozen.

What's the matter? Serah pulls away with a puzzled look on her face. "Light?"

She brings a hand up to brush Serah's face with her knuckles. That same hand moves to the back of Serah's head, threading strawberry-blonde locks between calloused fingers. "I said we can't do this." She lowers her voice. "I never…said I didn't want to." With that, she grasps a fistful of hair and captures the girl's lips.

Electric shocks jolt through Serah, ending in the fiery pit of her core. Her rigid body relaxes against her older sister. Lightning's kiss is gentle and awkward, the complete opposite of what Serah was expecting from the hardened soldier. The feeling is new to her; Serah has never kissed anyone before, and judging by Lightning's inconsistent movements, Serah figures her sister hasn't either. She shivers. Her hand rises to rest against Lightning's bosom and she feels the rapid pounding of a heart underneath. Is Lightning nervous?

Lightning gives one last kiss before she pulls away. The corner of her top lip rises for a second before returning to normal. Her face is flushed as pink as her hair, and she looks away.

Serah narrows her eyes in confusion. Did she do something wrong?

There's a subtle sigh before Lightning turns her attention back to Serah. She leans in for another crash of lips, this time with more confidence.

Serah melts under Lightning's lips and tongue. Hands begin to roam and explore her body and she follows suit. She trails her own delicate hands down over the soft fabric of a shirt. They rise and meet skin, moving this way and that. One stays flush against the front while the other moves to Lightning's back, running over every ridge and curve of her spine. Serah's caresses are slow and shaky, still unused to the intimate touches on another's skin. Thankfully for her, Lightning doesn't seem to notice.

The soldier begins to change course. Her lips descend, marking a trail of wet kisses down the girl's neck.

"Aah…" Oh. That was…new. Serah's body burns in ways she can't possibly describe. Her eyes shut. The lips on her neck rub, kiss, and nip at random - unpracticed gentle assaults. The hand on Lightning's back grips the shirt tight.

Lightning ceases immediately. "Serah? You okay?"

"Mmm. Keep going, please."

And she does. Lightning's teeth rake over creamy skin, finally stopping at the junction of Serah's neck and shoulder. She runs her tongue over the spot before doing the same to the area just above it.

"Oh, my…" She can't even finish. Do kisses on the neck always feel that wonderful? She's so mesmerized that she doesn't realize that Lightning has moved her, laid her down on the bed. Serah doesn't open her eyes until the feather caresses on her neck cease.

Lightning is straddling her, staring down at her with narrowed and focused eyes. Before Serah opens her mouth, Lightning descends and captures her lips. Her hands roam under Serah's shirt, tracing every inch of ivory skin.

A single moan escapes Serah and she blushes, her muscles twitching under her sister's touch. She shivers as inexperienced hands find themselves on her breasts. The fabric of her shirt tickles her heated skin as those hands trail up her torso. She lifts her arms without hesitation and feels the shirt being lifted over her head. Serah's top half is naked before Lightning. Granted, they'd seen one another without clothes, but this time is different, much too intimate.

The smallest smirk adorns the soldier's face as she takes in the view of Serah's breasts before her. She lowers herself and focuses her attention to one.

Serah throws her head back. Lightning's tongue strokes the underside of one breast before giving the same attention to opposite, rendering Serah speechless. She grabs a fistful of the hair that brushes her skin and bites her lip hard. How is it that Lightning learns so quickly?

Lightning grazes teeth over a hard nipple, while one hand is busy with the other between a thumb and forefinger. By now, her ministrations are more natural, faster and less random than before. She caresses each breast once before kissing a trail south between them and-

Oh, Etro. Serah bucks her hips under Lightning's tongue dipping into her navel. She can feel just how soaked her underwear is at this point and her face burns. Her body shakes with slight shudders. How can she get this wet over a simple roaming of hands? And even now Lightning's tongue is oh fuck…too close.

Lightning stops. She rises just enough for her eyes to graze over every feature of Serah's body. She grasps her bottom lip with her teeth and just stares. And…stares.

Serah knows her sister well but she can't decipher the expression on her face. Is she thinking of a next move? Is she going to stop completely? Serah's lips poke out in a genuine pout.

Lightning leans down to brush Serah's lips with her own. She kisses a path to her ear to whisper, her voice husky. "Please don't look at me like that."

The biggest ripple of lust courses through Serah at those words, ending at her already painfully throbbing center. Serah grasps each side of Lightning's shirt with a hand and yanks hard. Lightning complies and the shirt is peeled off, thrown carelessly onto the bedroom floor. Serah refuses to look away, marveling at her sister's upper half. She tilts her head to the side in piqued interest at the soldier's just barely smaller chest and sharp outline of her abs, both of which she never paid much attention to before.

Grabbing one of Serah's hands, Lightning guides it up her abdomen. When Serah catches the suggestion, she lets go. She sighs, moving her hips against the smaller frame beneath her.

Serah's mouth parts and her eyes stay fixated on her sister's body. Her hand roams and runs over the hard muscle beneath soft skin, the silver stud in her navel. So that's what it feels like? She admits to herself that she's been curious on occasion, just genuinely interested. Her hand rises further to cup one of Lightning's breasts. She squeezes gently and overall attempts to mimic her sister's actions from before. In the end, she receives the response she's looking for, a small strained moan and the rough gyration of hips.

Lightning lowers herself, resting on her arms with each hand on either side of Serah's head. Her breathing is labored and before long, she knocks Serah's hand away. Her face flushes as she stops all movements once again.

Now Serah understands. Her older sister is conflicted. But dammit all, they're too far in to stop now.

Lightning bites her lip again, hard enough to draw blood, and hangs her head.

"Light?"

Silence. Lightning ignores Serah's call, only to descend further down her body. She marks her skin with wet kisses before stopping at the waistband of pajama shorts. Her fingers drum on Serah's hips. She plants more kisses on the girl's heated skin and brings a hand up to cup the center of her shorts.

Serah gasps at the sudden movement, thrusting her hips into the strong hand. She thinks of every swear in the book to curse her sister into oblivion for teasing her so outright. "Ahh…sis, pl-please…"

Lightning runs her hand over the front of Serah's shorts twice. "Serah," she starts. She traces her fingers around in circular motions before dipping them into the front of the shorts past the underwear, brushing the soft, wiry hair below.

Serah whimpers.

The elder Farron knits her brows. Her voice is low and careful as she speaks, "I've…heard that it hurts."

Serah nods slowly. Yes, of course, she had heard the same. Too much of it, to be honest. There were more than enough of her peers at school bragging about how they'd lost their virginities to their so-called boyfriends, always explaining how the first time would hurt but slowly get better in the end. Would it be the same for her?

"You still want to?"

"Yeeessss…"

"I promise I'll try not to hurt you. If it's too much, then tell me to stop." Lightning leans down to peck her sister's lips.

Serah whimpers an 'okay' into the kiss. She lifts her hips and notices her shorts and underwear slide off. She's stark naked and at this point she truly feels it – the sheets beneath her brush every inch of her back, as cool as the air in Lightning's room. Her already stiff nipples become rock hard. And she's wet. Wet, wet, soaking wet between her thighs under the predatory gaze of her own sister.

Lightning kneels over her. She runs her hand down Serah's abdomen and drags a careful finger down the girl's slit. A dramatic tease at her entrance has Serah writhing violently under her. She stops, locking her eyes with Serah's. "Ready?"

Serah shuts her eyes, breaking contact. "Mmm…uh huh." Serah braces herself, biting her lip. That teasing finger plays at her entrance once more before venturing inside her, so painstakingly slow. Serah's gasp cuts through the room.

"Serah, you're…clenching. I can feel it. Try to relax, okay?"

She opens her eyes half way and responds with a quick nod. She can try, just try. And she does. At least she attempts to. That finger is sliding into her more easily now, but only just so much. There's minimal pain so far; Lightning, of course, has kept her promise, not that she doubted her in the first place.

"That's better. You okay, Serah?"

No response. How can she with a finger plunged so deep into her sex? Her body rocks, matching the steady pace of the appendage that slides in and out of her. A sigh escapes her as her head twists and turns on the pillow beneath her. Lightning chuckles above. How smug of her. Serah reaches out, waving her fingers against the night air to find the mane of identical, red-blonde hair. She can barely see with her eyes so low, but finds her fingertips threading through silk. Two rakes through and she's blessed to hear the soldier above her moan her name. Serah uses what little strength she has to pull Lightning towards her, eager for another heated kiss.

Lightning obeys without resistance. She kisses her mouth, her nose, her cheek, everywhere on her face before dragging teeth down the center of the girl's neck and kissing her right in the valley of her breasts. She sits back on her haunches between Serah's legs and slows her pace. She retracts her finger, gradually, to trace the sopping wet opening with an added digit.

Serah's lips part to allow a fragmented moan to escape. Lightning looks like a shadow in front of her, just barely touched by the glow of moonlight from the window. Serah finds herself shuddering under her glare. What power she holds over Serah with but a simple and primal look. But it isn't fear that shakes her from head to toe. It's trust. She trusts Lightning more than anyone on Cocoon and she wouldn't have it any other way. So she braces herself again, stretches her arms out over the queen-sized mattress, looks directly into deep blue-green eyes. Her vision grows hazy, blurs itself over the two digits entering her at a snail's pace. She clutches two fistfuls of bed sheets, bites her lip, arches her back. It hurts, no lie, and she tries with all her might not to cry out.

Before long, Lightning has two fingers buried within her with another massaging her clit. Once again, she hovers over Serah, scrutinizing her every shake and shudder, listening intently to her moans and sighs. She works up to an even pace and maintains it.

Serah breathes hard and releases a low moan, a sound she herself was unaware she could make. Lightning's fingers inside of her speed up just a fraction and catch her by surprise. Serah bucks her hips and arches even further. Lightning descends and Serah feels bare skin touch her front, nipples brushing over her own. Fingers run from her neck to her spine to hold her in place. Serah fits so perfectly under Lightning's toned body that she flushes, a warm red covering both cheeks and neck. A warm breath ghosts her ear, erupting gooseflesh over her entire body.

"Dammit, Serah. We- we shouldn't be doing this."

"I- mmm, no- you…" How pathetic. She can't even get the words out she's so high on ecstasy. After a short squeak, she wets her lips to try again. "I- I don't c-care. Need…you. So. Bad. Nnng, Claire." She hasn't uttered that name in so long and loves the way each letter caresses her lips and tongue. Lifting her hips in tandem with Lightning's rhythm, her knees rub hard against the outside of Lightning's legs, brushing the crimson nylon of Lightning's shorts against her inner thighs.

With her free hand, Lightning grasps one of Serah's, running her fingertips over an open palm before lacing their fingers. She lets out a half chuckle as she watches Serah writhe and shake under her.

Fire burns in the pit of her being. Every sense is on critical overload. Serah's body vibrates and thrums with a weird sensation she's never felt before, a multitude of feelings she's never experienced, not all at the same time. Elation, lust, confusion, disgust. She can't think straight – what is up or down, left or right, where is Lightning? Inside. A deep and guttural moan rips from her chest. The fire becomes white-hot, searing, until it morphs, changes. It shoots through her like a bolt of electricity, starting from her throbbing and aching core and touching every inch of her. Lightning.

Spent, she lies there and attempts to calm her breathing, chest heaving with a thin layer of cold sweat. Her vision begins to clear and she sees the dark figure of Lightning hovering above her, eyes and jeweled necklace illuminated by moonlight. She rests her legs against Lightning's own. That's when her thoughts return. What would their parents say from the afterlife, what would they think, seeing their two beloved children in bed together? Serah covers her face with her forearm, then with both hands. Hot tears stream down the sides of her face into sweat-damp hair as she weeps silently. She can't process what she's feeling, nor did she know in the first place. The bed creaks, signaling Lightning is moving, and Serah feels lips against her forehead. Strong, protective arms snake around her naked body. Lightning only speaks a few hushed words to her, and that's the last thing Serah hears before she cries herself to sleep.