It's not what she expected.
Sif barely even felt the needles, just a stinging flicker as the tip penetrated her flesh and another when it emerged a thumb's width away, and in between a dull sense of pressure as Loki drove the metal shaft beneath the surface. The pain faded quickly once the needles were in place, and Sif imagined that if she weren't looking right at them, she'd forget that they were even there. There was no blood to speak of.
She wasn't sure then how much her insensitivity owed to her usual high tolerance for pain and how much to the way Loki had numbed her skin with the chill press of his mouth before moving in with his fire-cleansed needles. He'd claimed the freezing was for her benefit, but Sif suspected that he enjoyed her uncomfortable squirming as he swirled his frosty tongue over her breasts such that he'd do it even when it was unnecessary.
Sif was not so numb that she could not feel the tickle of Loki's breath as he slid a needle into place, parallel to the one above it and mirrored on the other side. He glanced up at her and smiled, his expression deceptively mild, and reached for another needle, extending the even column marching toward her nipple from the top of her breast, starting just low enough that the marks would be concealed by the modest cut of her usual tunic.
The other Loki, the one who'd been peering from the chamber out into the corridor through the narrowly cracked door and giving no sign of attention to Sif and his double's delicate occupation, sighed and wandered back toward them. He smirked when he caught Sif's eye, torn by motion away from the slow tunneling of needle through flesh, and licked the tip of his right index finger.
“How do you like it so far?” he asked, leaning low over her shoulder. He gripped the back of her chair with his left hand and dragging his wet fingertip down the centre line of her body, between the banks of sharpened points.
“Well, my lord,” Sif answered, her voice rougher than she'd anticipated.
“Indeed?” His hand slipped lower, to cup her naked mound, and he purred at the wetness he found there. “You are wanton, aren't you?”
Sif grinned up at him as he stroked her cunt, then yelped when he slapped it sharply. The other Loki, the one with the needles, paused to give him a castigating glare. “She is meant to keep still for this part.”
Standing Loki rolled his eyes at Sif, and she suppressed a laugh, unwilling to disturb his artistry by moving before he was finished. She knew very well that talking to himself was a show put on for her entertainment and edification. “How much longer?”
“Nearly finished—nine and nine. I could do another set across her belly, but I don't imagine you'll be patient enough to let me.” Kneeling Loki finished impaling her left breast for the eighth time, and paused to admire his handiwork.
“Not me,” standing Loki said, regarding Sif critically. “Her. How many days, Sif, since you last brought yourself off?”
“Three, my lord.”
“You've done as I instructed?” Kneeling Loki looked up as he picked a weapon, ordinary sewing needles with sharp points and flared cyclopean heads, from the collection spread out on a cloth next to her chair. “Touched yourself with thoughts of me, but denied yourself completion?”
“Of course.” Sif's breath caught as the last needle slid into place. It hurt more, the closer he got to her aureole, though again Sif was unclear if that was because she was more sensitive there or because Loki's oral anaesthesia was wearing off.
The Loki standing over Sif with his hand between her legs abruptly hooked two fingers into her cunt, stroking her from the inside. His other hand slid over her shoulder to flick the outside ends of the needles sticking out of her right breast. Sif gasped and arched in her chair, her internal muscles clamping tightly around Loki's fingers as she winced.
Loki who pierced her chortled and stood up. “How's that?” he asked, nuzzling her ear as he dragged a thumb down her left breast, pressing down on the thin sheaths of skin overlaying each neatly stacked needle. He drew a finger back up over the outer ends of the needles, causing them to roll inside her flesh, and his eyelashes tickled her temple as he watched with two pairs of eyes for her reaction.
“It's,” Sif said. She shook her head, at a loss for words.
“Can you feel me inside you?” the Loki on her left asked, pulling on a needle so that its tip angled downward.
“Yes,” Loki echoed, while his double hummed approvingly. “You'll feel me for days after this, for as long as you wear my marks.”
Sif had expected at least one of the Lokis to lower his breeches or to will away his clothes entirely and fuck her—turning her to grip the chair's arms, perhaps, or taking her place on its seat and pulling her into his lap—but if this was in his plans at all it was not an urgent goal. Both Lokis appeared to derive adequate satisfaction from tormenting her with the needles—fucking them in and out of her flesh, drawing them back in their new-cut channels and pushing them deeper in; twisting and pulling them to stretch her hide; and flicking the raised skin that covered them; savouring the control that her reactions implied.
“Insatiate creature,” Loki breathed—not the Loki with his fingers sunk knuckle-deep inside her cunt, immersed in her wetness, but Sif supposed that didn't matter. “How patient you have been with me—do you suppose that you have had enough?”
“Yes, my lord,” Sif panted.
“You know what to say.”
“Please, my lord.”
“I wish to come.”
“There's my girl.” Both Lokis pushed their respective sets of needles in to the hilt, until their flared ends caught at the outer ends of the fresh-bored passages and Sif cried out at the burning, tearing stretch of it at the same time that Loki's fingers twisted to press at that swollen, spongey place inside her cunt, milking out her orgasm.
Loki withdrew his hand with a sigh, when Sif's clenching muscles finally relaxed enough to allow it, and reached to paint her face with streaks of her own abundant brine. His double laughed and removed the needles one by one, dropping them into wooden bowl. At last the blood came, welling up every place that a needle's point had broken her skin going in or out, thirty-six red beads of varying sizes swelling and shining and in some cases bursting and running in thin trickling streams down the slope of her shivering breasts. With all the needles collected Loki returned to himself, one of him shimmering out of existence and leaving the other to stroke Sif's hair with rough affection before lowering his face to lick at her ruby-jewelled bosom, suckling from the rows of puncture wounds and staining his cold lips with her hot red blood.
This is what Sif thinks about the day she watches them sew Loki's mouth shut.