I can understand not seeing a downside to this...

Derek was ready to tear his hair out.

Emma Swan was driving him crazy, in all the right ways...which were so wrong, because he really couldn't do a girlfriend right now, especially not one with a kid. She had a bounty to chase, he had a deadpool still making his life miserable long after it was dead and gone--none of this made sense or would work at all.

Except for the fact that they were playing house so she could nail her bounty and he could be done with these assholes who still thought there was a way to cash in on killing supernatural creatures.

Fortunately (and unfortunately), he had a night off from Swan, that knowing sister (cousin?) in her pack, and the deadpool. They weren't due to stake out her target for three more days, and he was alone for the night with a few movies, a couple of thick steaks, and the solitude he needed to mediate a little before the full moon in roughly two or three days.

So he took a shower, put the steaks on...and was just finishing them up, hair still damp and wearing only a pair of jeans when he caught a scent.

Frowning, Derek plated the steaks and crept silently through the loft. Reaching the door, he paused, listening...

Two heartbeats. Two sets of feet, one heavier than the other...the clean, sultry fragrance of leather and soap on skin...and another, warm cotton and the chemical sting of some off the shelf scented body spray for men...

Torn between confused and aggravated, Derek didn't wait for them to reach his door. Sliding it open, he stepped into the hall and waited until Emma came into view.

His expression immediately softened when he saw the male following after her.

"Emma?" he called out, leaning in the doorway and crossing his arms over his bare chest. "What's going on? What are you doing here?"

A week after Allison's funeral, Stiles borrowed some books from Deaton and Mrs. Yukimura. They all knew what he was looking for, but nobody said anything. They needed to be careful with Stiles, give him the space he needed to heal from what was done to him...and what he'd been forced to do.

Also, the things he was looking for, the things he wanted to do...they just weren't possible. And if they were...

Nobody really worried until roughly two weeks after Allison's funeral, a knock came at Derek's loft door, accompanied by the stink of the grave: soil, filth, death.

Shaking like a leaf, grave clothes dirty and tattered, a very much alive Allison Argent collapsed into his arms as the first rays of dawn streamed through his window.

Stiles insisted he did nothing. Deaton backed up his claim after checking and confirming that no primordial power had been tapped. Still, there she was, huddled in the corner of his loft without moving or speaking, letting no one touch her save for Derek and Lydia. It was Lydia who coaxed her from the corner and out of her filthy clothes, Lydia who coaxed her into the shower and helped her clean up.

She trusted only Derek to clean and tape up her belly wound, still bleeding but no longer fatal. When urged to dress, it was one of Derek's shirts she accepted, and Derek's bed she finally fell asleep in.

She trusted Lydia for obvious reasons, but Derek...perhaps some part of her remembered that he had saved her father. Perhaps it was his absence at the time of her death that made his presence less traumatic, none of them were sure. Lydia stayed over while Derek spent the night looking for answers.

Instead of answers, he found an Oni.

While the creature harmed no one, with every passing night, it seemed to grow in strength...and with every passing day, so did Allison. For every piece of her they gained, the Oni only grew in power, becoming a greater and greater threat with no master to control it.

The second day, Allison allowed her father to see her, embracing him with tears in her eyes. That night, the Oni attacked three Sheriff's deputies near the hospital.

The third day, she finally began speaking. That night, the Oni's blade stopped just shy of cleaving Scott's head from his body before the creature fled.

Each day, Allison grew stronger, more alive...went to school, laughed, returned to them. Lydia began staying at Derek's loft more often, and often all three of them ended up in bed, Allison sandwiched between two warm bodies. It wasn't sexual, it was Allison's inability to sleep alone any longer...she needed bodies, warmth, touch to remind her that she wasn't in her coffin, lost to the grave.

It was Lydia who noticed it at the end of that first week: how the Oni attacked at night...how Allison was never in bed when they woke up. She was making coffee or showering or nibbling on a bagel on the sofa because she didn't want to wake them...

Derek said nothing. He did, however, make plans to be out on the eighth night, and made sure the girls knew about them.

He returned to the loft around eight PM, just as the sun was setting. Allison fell asleep early these days, and Lydia was already curled behind her, arm slung around her waist and face hidden in the soft mane of curls Allison was trying to grow back out again.

And as he slipped inside, he arrived just in time to watch his worst fears come to life.

Allison's prone form began to melt, fading into black vapor that slithered away from Lydia's embrace and wafted across the room. When it coalesced again, standing erect, it bore the form Derek should have recognized. He'd attacked it once, on the fourth night...he should have known those slender limbs, suspected when it incapacitated him without going for the killing blow...

Now he knew why it hadn't killed Scott.

"Lydia!" he barked, hoping she was only dozing yet. "Lydia, wake up! It's Allison...she's the Oni!"

Derek slept on his back whenever possible. It was harder, sharing his bed with someone else, but once Allison figured out his habits, they found a comfortable arrangement: she'd either lay on her back beside him, his arm and leg draped across her body, or he'd lay on his belly and she would drape herself across him, cheek pressed against his shoulder or the center of back. In truth, he preferred the latter: being her man-shaped body pillow. Piling up that way felt familiar, the way he'd napped with his brothers and sisters as a child, the way he'd sometimes slept with Laura when the loneliness was too much to bear and they needed that warmth and the familiar safety of another body, carelessly sprawled in the dark.

After he got his tattoo modified, piling up with her in bed got impossibly better.

She took new pleasure in waking him up with it. Rising from the fog of sleep, he would feel the dry, silky brush of her lips against each spiral of the triskelion, and a kiss against each arrow that now connected them. Sometimes, if she felt playful, she'd let her mouth wander lower and lower until he finally rolled over and let her straddle him, already hard and ready to be guided into her body, to be ridden until they both shattered. Other times, she'd kiss her way up his spine until she was pressing her face against the curve of his neck, hands curled around his shoulders. Those were the times they made love more tenderly: lazy and slow, drawing out their pleasure until it exploded in a golden wash of pure ecstasy.

Derek loved it when the tattoo led to great sex, but he was more grateful for the times it didn't.

He never had an easy time falling asleep. Most times, he was content to lay there, eyes shut, until her breath leveled out and he was free to watch her for the rest of the night. Others, she seemed to have just as much trouble and would watch him.

Tonight was one such night. They'd fucked three times already, and he was deliciously spent but not nearly ready to sleep. He lay on his stomach, arms folded and buried under his pillow, eyes shut as he just drifted pleasantly.

After a little while, the hand he knew was coming brushed over his back.

It always started the same, a warm palm and gentle fingertips just resting over his tattoo, laying there, a feather weight against his skin. Then, slowly her palm would lift, and her fingers would map the lines, starting with the spirals. She'd trace every curve with the tip of her middle finger, the rest errant brushes of butterfly's wings until she'd finished. Then the arrows were next, her index finger running gently over each one.

And she would do it again...and again...and again. By the third repetition, her body was pressed against his side. By the seventh or eighth, her chin was a sharp, pleasant weight on his shoulder. By the twelfth, she'd shifted completely to stretch out on top of him, chin propped on an arm folded across his back. He didn't know how long she continued before she fell asleep that way, head pillowed against the middle of his back, but often in the morning, finding herself that way, she'd press her mouth to his tattoo instead and wake him up with kisses and slow, warm sweeps of his tongue.

Tonight, she was pressed against him after the second repetition of tracing the arrows. Third, and her head was on his shoulder. He wondered how long she would last tonight before she fell asleep, stretched out atop his back.

He didn't know, because it was those fingers on his skin, that wandering touch, that was his cure for insomnia, soothing and lulling him with every trail around the circle until the rhythmic touch was quietly drawing him into the blissful arms of sleep.