This is sort of AU as Light is somehow entirely missing... It's also a little OOC because Misa is secretly very into L... Don't think too hard about it, it's PWP...

Headquarters feels deserted at 3.00 AM and the buzzing lone computer he sits in front of only serves to accentuate that. Most of the lights have already been turned off leaving just one bright florescent bulb above him while the rest of the room sits in shadow. Even his breathing seems loud. Although, that may have been loud even at 3.00 PM.
On the screen in front of him is a woman lying in her bed, feet against the mattress and legs curved. Every time she moves her hips he nibbles on his thumb with just a little more intensity.
The room that fills his screen is only 20 paces up a flight of stairs and then 40 paces down the hall. All rooms in his building have video surveillance, and the question of morality is void when it comes to safety. Void even more so when it comes to him. He's L after all, and he wouldn't be where he is today if morality was a significant blip on his radar. Nor would he be here if he had tried with even a slight modicum of perseverance to deny himself what he wanted. Tonight what he wants couldn't be more clear.
The woman on the screen tilts her head back as her hands start moving faster under the blankets. Her normally perfect blond hair is splayed over the pillow looking more and more undone as she herself is.
Her mouth hangs open, her eyes tightly shut as she pants and occasionally whispers something under her breath. He can guess what she's whispering. Can guess what is going through her mind. Any one who knows her could. It's the Yagami boy.
For what seems like a long time he does nothing more than stare at her as the blankets slip off of her frame revealing soft skin and lovely curves. Her hands keep going, sometimes slowing then picking up the pace. Her skin is starting to develop a sheen of sweat, but lost as she is something is holding her back. Every now and then she seems close but then stops with a look of frustration before starting again. He should probably tell her that she could have anything she'd like sent to her, and since she's no longer a Kira suspect, it would not be examined by them. None of those things are true, but it might convince Misa to buy the toy she clearly needs.

He leans back, feet firmly planted against the seat and looks down at himself wondering if he should…
He rubs the outside of his jeans then, and yeah, that definitely feels good. Misa is nearly naked on his screen at this point, just some small part of the blanket draped over her lower leg. As if he prompted her, she stops touching herself between her legs, and moves instead to run her hands over her body. Softly at first, just fleeting caresses down her sides, over her hips, down her thigh, from her knee along the inner thigh all the way up… and then quickly away again. She moves to her breasts, using a little more pressure here, and that's exactly where he wants to see her hands now. She plays with her nipples, pinching them, like he would, between two wet fingers. And those delicate soft digits look good too, he wants to taste them. Taste her.
One hand stays on her breast as the other moves down and starts gently rubbing between her legs. And this seems to work, the muscles in her leg start to tighten up, her breathing becomes more labored than he'd heard it in the last 30 min, her hips start shaking a bit and she pants harder and harder, her back arches off the mattress, her pants become moans, until…

" Ohhhh….. Ryuu..zaki" It spills out softly as she nuzzles her face into the pillow.

L's world falls away for a few splintering seconds and then rushes back up with the intensity of a 9 story drop.
Not Yagami? Is the only coherent thing his mind can offer.
His eyes focus on the screen as if willing her to repeat herself, because he must have heard wrong.
She's stopped touching herself, body lax as she pants. It looks like she came already until she abruptly sits up and in sheer frustration hits her pillow and throws it to the other side of the room.

Still no luck then, Misa-san? L thinks.

He looks behind him then, to the stairs, and mentally walks the other 40 paces down the hall. He's half way up the stairs before he realizes what he's doing and once he does realize, he agrees with it.
He makes it to her room in record time and doesn't bother knocking. When he opens the door she's laying on her front, head pressed into the pillow and her arms around it, her back is facing him.
And those soft curves, those muscles underneath that flex and stretch and would do so beautifully under his guidance. He swallows.

"Misa-san?" He tries.

She whips around, now leaning back on her lower arms as her entire body becomes visible. And while there is a joy of its own to watching someone on screen, he has to admit that in this light, her skin looks softer and more delicate than the camera's could show.

"Ryuzaki!? What!?" She trails off and her eyes dart around as if looking for something to cover herself up with. Then she calms, looks straight at him with narrowed eyes and makes no further attempt to cover herself up.

" You were watching." She says. It's not a question.

"Yes." He replies unapologetically. She does have the uncanny ability to surprise him with unexpected insight at times. He walks up cautiously, but determined. His eyes eat up every inch of exposed skin and linger on the curve of her hip to imagine his fingers gripping them tight and pulling them flush against his body.
Misa watches him warily, like an animal unsure of its safety and ready to strike. L sits down near the foot end of the bed, and gently caresses her ankle.

"I saw Misa-san was having some trouble and thought she might like help."

Misa seems torn between fuming and resignation. L is pleased when her eyes soften and it becomes clear the latter has won out.

"Ryuzaki-san is a pervert. I always knew it." She pouts. There's no rancor in the statement. She looks up at him through her lashes, her lips pink, wet and swollen from biting them.
And he never claimed to be a saint, or even remotely morally sound, nor has he claimed to be patient, so her takes her face in his hands and kisses her then. Long and deep as he pushes her back into the mattress. His hands rove over her body grabbing those hips and pulling her thighs to move around his hips, and she obeys so instinctively, he groans in the back of his throat.
She's laying completely naked underneath him while he is fully clothed, and this will prove problematic in the long run, for now he rubs his rough jeans in between her legs just to watch her squirm. And she does, her hips tilt up against his to get more friction and her hands press his body closer, nails already pressing in through the fabric of his shirt.
He nips at her lips, then moves to her neck to slowly suck on the sensitive flesh there.

"Ryuu.." she pants, her hands moving under his shirt tracing over the well defined muscles. He starts moving faster, loosing himself in the way her body bends underneath him, the soft pants and chokes in his ear. Her smell engulfs him, sweet and musky and he buries his face in the crook of her neck. Ohh how much he want to throw his clothes of and loose himself completely in her. But not yet, he pulls back.
And seeing her laid out before him then, legs spread, face flush, wetness coating her inner thighs, he almost forgets he has any willpower at all.
Quickly, and before he can succumb to the sight in front of him he tugs at his pants, unzips them and slides them halfway down his thighs, freeing his erect member and holding it out for her.
She seems to immediately understand his request and a hunger washes over her face like she's craved this as often as he'd pictured it…
She takes it gently from him then, and with two hands starts slowly pumping it, her mouth traces the tip and shaft whenever her hand are busy elsewhere, her tongue darting out quickly at first, and in long languid strokes later. This rush of her wet tongue and lips, alternated with her hands pumping him slowly makes his head go fuzzy and his hips start jerking of their own volition. She steadies him with both her hands at his hip bones as she takes him into her mouth slowly, so slowly and wetly, deeper and deeper. When he hits the back of her throat he buries his hand in her hair and tries to hold back from bucking into her mouth.
Fuck, she feels so good.
As if she feels his restraint and wants to break him she starts sucking and her tongue moves around all of the most sensitive places and he's going to come!
He stops her motions and slowly pulls out, the tip lewdly resting on her bottom lip before he pulls it clear.
And she look at him with a desire he didn't think possible and moves to reclaim him. He understand it then.

"Not yet, Misa. If you want it you'll have to wait for it." It comes out low and raspy, very nearly a growl.

Her eyes turn to molten lava then, and if he ever believed he had not heard her moan his name, this look would make him pause in that assumption.
L wastes no time in taking his clothes off and within seconds he is naked, hovering over Misa who squirms eagerly beneath him.

"Please… Ryuu!" she begs, " I need you"

he grabs her thighs, pressing his fingers into the soft skin and watches intently how her eyes glaze over in anticipation, her lips quivering.
He positions himself and slides into her in one smooth motion. Misa gasps and arches her back into him, her head tilted back. She is so wet, so very, very wet there is absolutely no resistance as he pumps into her slowly at first but quickly increasing, going in long deep strokes.
He put his hand at the base of her spine and tilts her hips so he can plunge in as far as possible and, oh fuck that feels good.

"Ryuu!" Misa exclaims, desperately trying to tilt her hips up even further and meeting his thrust with her hips.

The sound of him crashing into her fill the room and in the complete silence that covers the building, he thinks this might be the most lecherous thing he's ever heard. He goes harder, and harder, unable to stop himself now, so lost to the feeling and Misa crooning underneath him, all smooth lines, soft skin and deviant tongue. He feels it building underneath his skin, making every point of contact tingle with anticipation. And Misa is digging her nails in the the planes of his back, drawing blood, but he can't care. He vaguely believes he hears her then, chanting his name over and over until he feels her shudder, her eyes shut tightly and trying with all her strength to keep him closed inside her and he does loose it then. He rams into her watches how her body slides over the bed and her head rattles the headboard with every thrust, but he's lost, he can't stop, he feels it rushing through his body and when he comes it's hot and light, and furious, full of frustration and want , and fuck, she has no right to feel this fucking good, and he fills her.

He looks at her then, his hair sticking to his face, body sweaty and bloody. He'd always thought Kira would leave him sweaty and bloody, he just never envisioned it quite like this. He turns to pull out of her and catches his breath for a few short moments.
As if both of them are too afraid to speak for fear of acknowledging what just happened, they stay quiet, each on their own side of the bed.
L moves to get up and leave, but before he can Misa grabs his wrist.

"Don't", she simply says, "Misa might need you again later…"