Zuko dreamt of a witch.

In his dream he saw her standing on the tundra. The blue-white ice was flat and endless, and gleamed as bright as bone under the winter sun. There was a wild wind howling. As the witch walked towards him, great swathes of snow lifted up from the ground with the force of the breeze and clutched at her ankles, hungry for attention. But she paid no mind to the snow. She only had eyes for him. And oh, those eyes: the witch had true Water Tribe eyes. Blue as the bitter deep. Blue as the watery graves of a hundred thousand good Fire Nation soldiers. In her dark face they shone as bright as cut glass.

Don't come closer, he tried to say. But he found his mouth was numb. He touched unsteady fingers to his lips. They were frozen shut. He realised he couldn't stand – he couldn't run away. The ice had fused to his legs, pinned him down as tight as prey caught in a trap. The witch didn't have to use her dark tricks on him to hold him like a puppet. No, she'd already cut his strings. There was no escape.

She knelt down in front of him. Even though she was dressed like a waterbending witch, in deep blue-black, he realised she was no old Master. In fact, she was young. A woman grown, but not by much, with soft features and a wide, dark-lashed gaze. If it weren't for the long, pale scar bisecting the left side of her face, she'd have been quite beautiful.

The witch lifted a hand. Hesitated. He saw her mouth part: saw her moving to speak, too touch him, and then –

Then he woke up.

"Oh good," drawled a voice. He leapt up out of his bedroll, turning sharply towards the sound, disorientated from his nightmare. It was just Azula. She was leaning against the wall, arms crossed. She already had her battered brown parka on, the hood lifted up to obscure her face. But he could see her grin, all sharp white teeth. Shark-like. "I thought I'd have to zap you awake. See?" She lifted her hand airily. Lightning crackled on her fingers. "Zap."

"Stop that," hissed Zuko. "What if someone sees you?"

"Then I suppose I'll have to kill them," Azula said, unwontedly cheerful. "Stop being such a bore, Zu-Zu, and get ready. We're leaving."

"We've only been here a day," Zuko protested, even as he began packing away his bedroll with the quick ease that came from experience. "Another night and then we can catch a boat to – "

"No," Azula cut in. "I think it'd be better if we left now."

Zuko paused. Just for a moment. Then continued packing. Azula gave a low sigh.

"Oh, don't fuss," she said.

"I didn't say anything," Zuko said. His voice was brittle.

"I didn't kill anyone," said Azula. "Never fear, dear brother. I keep my promises."

"When it suits you," muttered Zuko. For a while, he kept his gaze steadily averted from hers, focusing on the task at hand. But then finally, unable to hold out any longer, he looked at her.

She was staring at him with bright, unblinking eyes. Was she cataloguing his weaknesses or just thinking quiet thoughts? It was hard to tell with Azula.

"It still suits me," she said, turning towards the door. "Are you ready?"

Zuko hefted up his pack. He touched his fingers lightly to his lips. His mouth was unmarked, lips oddly cool.

"I guess I don't have a choice," he said, and followed.

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Zuko was loyal to his sister, but it was a loyalty tempered by his awareness of the darkness in Azula's nature. Did she love him or simply tolerate him? He didn't know if she was crazed or simply canny; naturally sadistic or just twisted up by the need for revenge. The time before the long winter was a blur to him now. The fog of childhood had swallowed it up. If Azula had once been a sweet and soft-natured thing, Zuko did not remember it.

He supposed he'd once been an innocent too – but who could tell? All he knew was that Azula was now unpredictable and too powerful for her own good. She had the strength to hurt, to kill, and relished using it. And she had hurt Zuko – more than once. He had no reason to trust her, beyond blood. And anyone who had met a waterbending witch knew that you couldn't trust your own blood.

It was your blood that enslaved you.

But Azula had made him a promise; and once, long ago, on the night when the long winter began, Azula had saved his life.

It was the running he remembered best from that night. They'd run for what had felt like hours, run until Zuko's lungs ached as if they were smoke-scorched and his feet bled. His family had hidden with their most trusted servants in the catacombs under the palace, but the Water Tribe warriors had filled the tunnels with water and, terrified of being drowned like rats, they'd fled into the open.

Zuko had watched his father die first. He'd closed his eyes before they'd reached his mother.

They'd been trapped, the two of then. He and Azula. They couldn't have run anymore. The palace marble had gone slippery with ice. They were shivering. As warriors with painted faces closed in on them, Azula had tried to raise fire with her fingers. Tried, and tried, and tried again. But it was too cold. Too cold.

"Use your bending," hissed Azula. "Come on Zu-zu, help me."

Zuko couldn't. It felt like the fire in him had been snuffed out. He didn't know how it had happened. But his insides were cold. Something had died within him. There were no flames to reach for anymore; no breath of life to fill his lungs.

But he'd had his blade. The blade his uncle the Fire Lord had given him. A fine strong Earth Nation blade. He raised it and held it steady.

"Useless," Azula said, scornful. "You can't fight them with that. They'll kill you."

"Then I'll die with honour," Zuko said quietly, with all the bravery left in him.

Azula's eyes had narrowed, full of hate and fury.

"You think I'm going to let the Water Tribes kill us like animals?" For the first time Zuko saw there were tears frozen to her cheeks, thick as clusters of stars. They were tears of fury. A child's tears. "No. I REFUSE."

The room filled with blue light.

Lightning.

There was a great deal of death that night. But Zuko and Azula lived, and ran for their lives, and never stopped running.

Without Azula, Zuko would have died. It was a debt that bound them together permanently. As they trudged away from the village they'd been staying in, towards a new city, Zuko turned to look back at scorched, silent fields and dead livestock, and remembered.

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Katara returned to her body slowly. Gently. She modulated her breathing. In out in out, keeping a steady rhythm just like she'd been taught. She stretched out her senses, binding herself back to the physical world. She felt the soft cloth of the sheets beneath her. The prick of light against the closed lids of her eyes. The gentle rocking of the ship as it moved with the ocean. She felt it all.

Then, finally, she opened her eyes.

There was a servant kneeling by her bed, carefully setting out some provisions. Fresh fruit, newly baked bread. Sokka must have stopped at a harbour market while she dreamed.

How long had she been gone?

"Welcome back, Master Katara," the servant said, bowing her head. "Your brother asked me to bring you a food."

"I told him I didn't want to be disturbed," said Katara, and winced when the servant flinched. "No, no, it's fine. It's not your fault. I'll deal with my brother."

"I didn't mean to cause trouble – "

"It's fine, really," Katara cut in hastily. "Just. Can you tell me how long I was gone?"

"Two nights, Master Katara," the servant said, some of the tension leaving her. Then, after a moments hesitation, she raised her gaze and said timidly, "Did you have deep dreams?"

Deep dreams.

She remembered the man caught in the ice. Her ice. The cold panic in his bright eyes; the sharp twist of hatred to his mouth. The way he'd slipped away before she could touch him, her fingers touching the gossamer afterimage he'd left behind in the air. She'd been so very close. Just a moment longer, and he'd have been hers.

"Yes," Katara said softly. "I think I did."