He was always so cold.
In retrospect, this should have tipped her off to his true nature.
No matter the place or circumstance — the heart of summer on a world at the edge of a star or the shadowy corridors where they shared breathless embraces in their youth; exhausted in a field of dead foes as the heat of battle still buzzed in their veins or spent from another kind of exertion as they collapsed in their shared bed — she ran hot and he ran cold. Even the feel of him as he moved inside her was unique. Other men she'd been with —Æsir, Vanir, Midgardian — during infrequent breaks over their many centuries-long courtship had never quite satisfied. There was something dirty about the feel of their hot, sticky bodies writhing over, under, beside her. Not a good kind of dirty, like the feel of mud and blood flying up to meet her skin as her sword found sheath in living flesh, but a nasty, profane dirty, like the putrid stench that clung to the bodies of her fallen comrades as they lay slain in piles of filth, their bodies desecrated by burrowing maggots and clawing vultures.
But not him.
He was ice, always.
But he was also a prince, and Sif had no reason to doubt his parentage, no inkling that Loki could possibly be anything other than a true son of Odin. So she ignored the prickling of her skin as he wrapped himself around her; chalked the goosebumps that rose on her forearm when he touched her hand up to silly girlish whimsy — a rarity for a warrior of her temperament but certainly easier to believe than a prospect so outlandish that it never even crossed her mind.
And even when she knew what he was, she didn't realize that the signs had been there all along. Even as she stood before the All-Father after Loki's fall, screaming, crying, begging for the truth — things she never imagined she'd do before her king — even as she threw her sword at his feet and declared her loyalty to Asgard, but not him — never again him — she was blind to the truth. When she turned from Odin in anger, when he spoke with such an uncharacteristic softness as she started to leave, when he stopped her in her tracks with his words, when he whispered the truth so only she could hear, even then she could not see that the cold had been there all along, in the blood running through his veins, in his very essence.
It only clicked much, much later. After Loki's betrayal, after the Queen's death, after the destruction of their home world. As Sif spent a long, desperate night on Midgard. Earth. A city named Atlanta in a place called Georgia, where the heat was so oppressive that it clung to her skin like a shroud threatening to suffocate her. It wouldn't be so bad, she'd been told, if Thor hadn't accidentally broken the device that controlled the temperature. It was three more days until the start of the summit that had brought them there, but Sif felt she wouldn't last three hours if she couldn't find a way to cool down.
She rose from the bed where sleep had eluded her, stepped over the twisted, sweaty lump of sheets that she'd thrown from the mattress earlier that evening, and ventured out to the kitchen of the large apartment where Thor and his friends would be housed for the next week. Sif moved silently, leaving the lights off as she went along, thinking she might trick herself into believing the dark would bring the cold, as if association alone could lower the temperature. She grabbed a glass from the cabinet, blinked rapidly when blinded by the glaring light of the freezer as she extracted a handful of ice cubes from their tray, and closed her eyes as she ran the tap to fill her cup. She could almost picture an icy waterfall pounding against a pile of rocks and the room seemed to cool slightly. Sif lost herself so far in her fantasy that she jumped, startled, when the water overflowed to splash her overheated skin. She turned off the faucet and began to drink, taking long, desperate gulps. She felt better with every sip, as if the cold water was working a miracle, cooling the whole room. Her skin began to prick with cold but it wasn't until she felt a long-absent yet achingly familiar presence behind her that she knew it wasn't the water that was responsible. It was him.
Sif turned to look at Loki. Her gaze ran over him from head to toe as so many thoughts and emotions ran through her mind. She was furious at him for what he'd done to Thor, to Midgard, to his own fathers. She was scared of how he might have changed. She was distraught over the way he had left her. She was thrilled he was here, finally, standing right in front of her close enough that she could feel his presence though he remained apart from her, hesitant to reach out and touch her for fear of how she might react.
She hated him.
She loved him.
The heat was too much and he was so, so cold.
Later that night, many frustrating, satisfying, invigorating hours into their reunion, as he lay beside her stroking her arm, as he explained, slowly, painfully, that he had stayed away so long because he was afraid of how she would treat him when she learned her lover had been born of the monsters she had been raised to fear and hate, she realized for the first time that much of what drew her to him was rooted in what he was.
He was refined and restrained where she was raw and passionate. He was logical and she was impulsive. He liked to analyze while she liked to fight. He was Jotun and she was Æsir.
She was fire and he was ice.
They were a perfect balance.