Bring me the heart of the last waterbender.

This was impossible.

Bring me the heart of the last waterbender.

Why? Why ? Why her? How could this be?

Bring me the heart of the last waterbender.

Zuko clamped a hand over his wide-open mouth, trembling all over. His heart was racing, his pulse roaring in his ears.

Close your eyes, he told himself. Try to slow down your h—

Bring me the heart of the last waterbender.

He couldn't. Couldn't move, couldn't breathe, couldn't speak, couldn't calm down, couldn't stop looking at her. Katara's expression was beatific, her face tilted upwards to the moon, basking in its cool light in the same way that Zuko would turn his face towards the sun. The water droplets twinkled, refracting the Southern Lights, covering the whole courtyard in tiny circles of blue and purple that shifted and swayed with the aurora above. Katara smiled joyfully, her eyes full of wonder, clearly relishing the beauty of it all; she was ethereal, unhurried, bending just for the art of it. As Zuko watched, her grin became mischievous, lower lip caught briefly between her teeth; then, with a flick of her fingers, every droplet exploded into mist. He flinched violently as the spray hit his face, a gasp escaping from between his fingers before he could stop it.

No!

But it was too late; Katara looked over, their eyes locked, and her expression vanished. She took two leaping steps across the surface of the pond before landing on the ground, and Zuko prayed to every god he'd ever heard of to just get moving, please, please just run—

His feet finally got the message and he pushed away from the wall, running as fast as he could, deeper into the depths of the fortress, as Katara called after him:

"Wait! Zuko, please, wait!"

No , he thought as he rounded a corner and ducked through the gap between two absolutely gigantic doors, pushing them shut behind him with a groan. He turned to find himself in a ballroom, bigger than anything the Fire Nation Palace could possibly offer, its ice block parquet floor shimmering in the moonlight. All around him, the water vapour from the walls curled and wafted, reaching out for him with tiny tendrils.

Zuko felt his pulse pounding in his throat, his head spinning and his knees threatening to fold where he stood. He staggered to the wall, leaning on it for support as he pushed himself through each next step, overwhelmed with thoughts of keep going, don't stop, get out.

"Zuko!" she was still calling for him, chasing him, going to catch him.

His heart was so rapid, every beat echoing through his body, as if his veins were all pulsing along in time with it. He reached the other side of the ballroom and slipped through the first door he saw, into another hallway, which led him to a grand foyer with twin staircases curving up to— a second floor? Agni, is she serious? Doesn't matter. He scrambled up the stairs, almost on all fours, unable to trust himself to walk without collapsing.

No time. No time. No time. Keep pushing, keep going, one more step, one more—

"Zuko, please!" Katara cried, closer this time, and at the sound of her voice his focus slipped for a fraction of a second, but it was enough. His knees gave out and he went sprawling across the ice floor, sliding until he hit the wall with a faint thud .

"Zuko?"

He looked up to see her standing at the other end of the hall. As she approached, he pushed himself up on shaking hands, panting from the exertion, as the most curious feeling began to spread through his core. Despite the fact that Zuko was lying on a floor made of solid ice, his limbs weren't chilly; but his chest felt deeply, profoundly cold, and his heartbeat was sluggish, trudging, slowing— stopping?

Right at that moment, Zuko felt his lungs collapse. He looked down, pawing at his tunic, fingers grazing against skin that was frozen and blue like a corpse.

Every time your heart beats, she'd said. The ice crystals will form.

He gasped for air, trying and failing to fill his lungs, and his vision began to swim as Katara reached him, her hands reflexively flying to her side only to come up empty.

The spirit water, Zuko realized, as his mouth opened and closed like a fish. She doesn't have it.

And then: I'm going to die here.

She knelt down in front of him, reaching forward; Zuko couldn't shrink from her hand, so he could only watch as Katara pulled open his tunic, hovered her palm a few inches above his heart, blew a strand of hair out of her eyes, and then closed her hand into a fist and tugged.

Zuko arched off the floor, screaming soundlessly as something in his chest seized and was pulled impossibly tight, as if the very cells themselves had gone rigid. Then the cold feeling began to dissipate; he could suddenly breathe again, his teeth chattering violently, every movement pure agony. Katara's face filled his field of view, and she cupped his face gently in her hands.

"Breathe," she whispered. "Slow and easy. And if you feel like passing out, don't fight it."

She brings warmth, Zuko thought, and then the pain overwhelmed him and pulled him down into the dark.

.

When Zuko next opened his eyes, he was in a bedroom—a different one from the place he'd spent the past few weeks. This one was much larger, the bed huge and lush, surrounded by four posters made of ice with draping fabric hung in between. His whole body felt like it had been fed through one of the Fire Nation's huge wall-destroying drills.

Katara was nearby, curled up on a chaise lounge that wouldn't have looked out of place in Zuko's own chambers at the palace in Caldera, but for the fact that it, too, also seemed to be made of ice. She looked asleep, her face illuminated by the moonlight; but upon hearing Zuko stir, she opened her eyes and looked at him as if she'd been waiting for hours. They regarded each other for a while in silence, and then she sighed.

"You're an idiot."

Zuko would have screamed if he had the strength; as it was, he could only gape at her. "Are you fucking serious? "

Katara scowled. "You can't go running off like that, all panicked and erratic! Your heart was starting to freeze solid!"

"No thanks to you!"

If glares could cut flesh, Zuko would be ribbons. "I saved you, dummy. Again . You're welcome, by the way."

"What did you do to me? With the, um—" he curled his hand into a fist and made a sharp yanking motion.

"I melted the ice crystals," she replied. "All of them, all at once."

Zuko groaned as he remembered the awful taut feeling in his heart, and the shift as it vanished all at once; a shudder of pain went through his whole body. "What is wrong with you?"

"Nothing!" she snapped, jumping to her feet, her voice echoing through the room. "There is nothing wrong with me. And stop yelling; you shouldn't be exerting yourself, remember?"

"Well you shouldn't be—" Zuko faltered, then regrouped. "Also, you're the waterbender?!"

Katara exhaled a shaky breath before nodding. "Yes. I'm the last waterbender of the Southern Water Tribe."

Bring me the heart of the last waterbender.

There she was. She'd been under his nose the whole time.

Agni. Zuko tipped his head back against the headboard. He should be interrogating her, dragging her back to where he kept his swords, getting the deed over and done with so he could go home. Instead he was sitting here, barely alive, in her house, his life now indebted to her twice over.

She's close enough to take down and I've got the constitution of a wet noodle. Just another day for Prince Zuko, soon-to-be-former-Royal Failure.

Zuko shook his head, clearing the thought before he could dwell any more on it, and fixed his glare back on Katara.

"You lied to me," he rasped.

"I know. I'm sorry," Katara replied, coming over to sit on the edge of the bed, either not noticing or not caring when he flinched away from her. "You have to understand, I'm a secret. No one can know who or what I am. All the adventurers who make it this far, I just heal their frostbite and send them back on their way. None of them ever know."

"Well. The honour is all mine, then, I guess." Zuko couldn't keep the bitter edge out of his voice. "So, while we're being honest: why have you been faking healing me with that spirit water this whole time? Why didn't you just do this—" he gestured to his chest "—when I first got here?"

"The spirit water is real," Katara said. "I couldn't risk using my bending on you, not so obviously; the spirit water makes the process less...abrupt. And I would have continued doing that, but...well. No secrets during an emergency, I suppose." She looked down, fiddling with the edge of a quilt. "It's not a permanent fix, by the way. Your heart is still frozen; the ice crystals will come back. I'm working on it. I don't think there was any damage to the soft tissue of your heart, but I'll have to check later—"

He was already shaking his head. "No," he whispered. "No way. I'm not letting you touch me ever again."

Katara stopped fiddling, her expression unreadable. "So be it," she murmured.

Zuko scowled. "Really?"

"I'm a healer. I respect your autonomy."

"Some healer you are," he grumbled, mostly to himself. "You damn near killed me."

"Well that wouldn't have happened if someone had stayed in his room like he was supposed to," she retorted.

"Well maybe if you hadn't lied to me from the moment I saw you, I wouldn't have been suspicious! Ow!" Zuko yelled, as his heart twinged painfully. Katara huffed.

"Would you please calm down? I promise I'm not going to hurt you. I'll answer your questions."

He couldn't help but cock an eyebrow at her. "Oh, so now you're going to be forthcoming?"

She spread her hands, palms upturned. "I don't really have a choice, do I? You're not supposed to know who I am, and you do, so now I have no idea what to do with you."

Bring me the heart of the last waterbender. Zuko had an idea of what to do with her, and at that moment he couldn't tell if the task seemed especially horrible in light of this new revelation, or whether it had always haunted him and he was in too much pain to pretend otherwise.

I'll answer your questions. That's good; he had about a million of them. He always seemed to, with Katara. She created more mysteries than she solved, and it was fucking infuriating. Where to even start?

Zuko squinted. "How come you don't look a hundred years old?"

Katara chortled. "Because I'm not?"

"...what?" he blinked. "But, I thought—isn't the last waterbender—how could all the stories exist if you're so young? What about that story of how you ran away? Of being engaged to someone from the Fire Nation?"

There was a flash of something sorrowful in Katara's smile. "That all happened," she replied. "But it didn't happen to me."

Why do girls always talk in circles like this? Zuko would have thrown up his hands in frustration, if he could lift his arms. Katara swung her feet up onto the bed, leaning against one of the far posts and crossing her legs at the ankle, and Zuko snorted derisively.

"Making yourself comfortable, aren't you?"

She gave the facial equivalent of a shrug. "What can I say? I like this room."

"Well you sure do have a lot of them."

"Mm. Yes, I suppose I do."

His eyes narrowed. "Did you build this place?"

Katara shook her head. "No. My grandmother did. Well, my adopted grandmother."

Zuko blinked. "Your...what?"

Now Katara broke eye contact, her tongue coming out to wet her lips. "The story I told you was true," she said. "A hundred years ago, the last waterbender of the Southern Water Tribe was promised to a Fire Nation noble. Her name was Unne, and her betrothed was a man named Roku."

"Roku?!" the word escaped from Zuko's mouth before he could stop it, and Katara narrowed her eyes suspiciously.

"Yeah. You know him or something?"

Fuck, Zuko, will you ever learn to shut your big mouth? He cleared his throat. "I, uh. I'm familiar with the name."

That raised eyebrow of hers was going to be the death of him. "Learn that from your travels, did you?"

"I had a lot of interest in Fire Nation history," he replied, because it wasn't technically a lie. "For a little while, anyway."

Katara seemed to buy it. "Well. Unne and Roku, they didn't hate each other; not the way people say, anyhow. It seems that at one point—before Fire Lord Sozin's war transformed him into a mass murderer—Roku did possess some kindness and empathy. I think he did care for Unne, and she cared for him, but she knew she could never go through with the arrangement. She held a secret that not even the Tribe elders knew; something passed from waterbender to waterbender, and never shared with anyone else. And so, just before the Fire Nation delegation was set to depart, Unne ran. She came here, and she built this place, to shield herself and the ancient secrets of the waterbenders from the rest of the world. But Unne brought with her a brand new secret, too: she was pregnant."

"Oh," Zuko said. That was all he could say.

"She gave birth to a daughter, Hama. And for seventy years, the two of them lived here, cut off from the rest of the world. Unne passed down to Hama all of her knowledge."

"And Hama is your mother?"

There it was again, that flash of sorrow, or perhaps something even harder. "No," Katara replied, a hair too sharply. "Hama was not my mother. When Unne died, Hama was well past her childbearing years. She was powerful too, maybe even more powerful than Unne. She was able to seek and find power using her mind's eye, able to pull water out of things you wouldn't imagine. So she kept tabs on all the Southern Tribes, searching for a baby girl who was a waterbender, and when the opportunity came, she...took it."

Zuko swallowed the lump in his throat. "Did you know your fami—"

"—I was an infant. I've only ever known this," Katara gestured around them. "Hama raised me, taught me, showed me everything she knew. She died, a few years ago. And I've been here alone ever since."

Zuko's heart jabbed him again, and he winced.

"Careful," Katara murmured, coming forward again to sit on the edge of the bed by his leg. "Don't overdo things."

"I'm not," he mumbled.

Her sigh seemed to hold the weight of the entire fortress around them. "So. Now you know what I am. The last waterbender."

"I suppose I do. And I'm—" Zuko stopped as Katara's face fell. "What?"

"Leaving."

He glared. "Pardon?"

Katara looked up to meet his eyes, and he was struck with how vulnerable she looked. "You were going to say that you're leaving, right?"

Was he? "I—"

"—please don't go," she blurted, squeezing her eyes shut as if the words hurt to speak. "Please, Zuko. Please don't leave."

It wasn't the sorrow in her voice that gave him pause; it was the fear. The quiver of her lip, the way her whispers were edged with tears, the wavering tone that gave away just how hard it was speak those words out loud. He swallowed.

Bring me the h—

—oh, shut it, I know. Let me think for a second. He furrowed his brow, trying to reconcile the Katara in his mind—hemming a sleeve, laughing over breakfast, hands steady on his chest—with the inconceivably powerful bender sitting before him, whose death was the key to the rest of his life.

No matter what happens, I'll make sure no harm comes to Katara, he'd said. Every part of his rational mind screamed that harming her was exactly what he'd have to do, but try as he might Zuko couldn't summon even a tiny flicker of anger, never mind the homicidal state he'd have to occupy in order to fulfill his destiny.

He was exhausted. It seemed to happen a lot, with Katara around. He had to grant that it was a pretty effective way to extend her own life, even if she didn't realize it. The revelation of her identity didn't change the mission; it just made things a whole lot more complicated, and sometime soon—when he didn't feel like he'd been run over by a tank—Zuko was going to have to ask some horrendously difficult questions. Why had his heart frozen, and not any of the others? What good was his honour if it meant killing a smart and sweet girl like Katara? What good was his honour if it came from killing anyone in cold blood?

Bring me the heart of the last waterbender.

He could never forget what he saw, but why did part of him wish she hadn't said it out loud?

Out of all these questions, the mystery why she wanted to keep him around was perhaps the least horrifying to ponder, and the curiosity was just too strong to resist. Zuko sighed.

"Give me one reason to stay."

"You'll die if you leave."

He shook his head. "Not good enough."

Katara fixed him with a very familiar look of exasperation, and a small part of Zuko wanted to smile even as her glowering intensified.

"That's not good enough?" she asked, and against his will Zuko's mouth turned upwards. He bit his lower lip until the urge passed.

"No," he finally replied, short and sullen.

"...I'll kill you if you try to leave." From the quavering in her voice, it was clear that Katara didn't believe that any more than Zuko did, and now he did smirk.

"I'd like to see you try."

Her hands clenched and released. "I can heal you."

"So could another healer. I know some very good ones."

Katara wrapped her arms around herself, and somehow in that moment seemed younger than her years. "Fine. The truth is…I need your help."

He laughed, just once. "What could you possibly need from me?"

The light of the full moon streamed in through the window, and Katara turned her head towards it, just as she had in the courtyard. "I draw my power from the moon," she explained. "I don't know if you knew that. I don't know how much you know about waterbending. And—well, you've noticed that it's dark pretty much all the time right now, but it's not going to remain that way. In a few months, the season is going to change, and the sun will come up, and it will be daytime for half the year; I'll still have my abilities, but I won't be as powerful." She looked back down, shoulders sagging. "Last year, when the summer ended, I had a vision that a monstrous man would come to this place, and when the sun rose again, he would cut out my heart."

Oh, Zuko thought. ...oh.

Katara sat up straight again, and wiped an invisible tear from her face. "Anyway. The vision showed me that I can't defeat this man, not as I am right now. I saw your swords, and I thought...you know how to use weapons, how to take down an enemy the old-fashioned way. I can bend, but I—I don't think it's going to be enough. I know it's a lot to ask, for you to fight a battle that isn't yours, but...if I can heal your heart, and maybe even your bending, would you stay and help me defeat him?"

Zuko was still too stunned to say a word.

"You don't have to answer right away. I'm sure you have more questions," Katara said. "For now, you should rest. You should recover fairly quickly, if you behave." She stood up from the bed without looking at him, and walked towards the door.

"Wait—" he blurted, and she turned back.

"Yeah?"

A million questions. Always a million questions, with her. Never anything simple. Zuko swallowed.

"Where am I right now?"

At this, Katara's mouth pulled upward into a half-smile.

"You're in my bedroom," she answered cooly, "for the first and last time."

And then she left, and Zuko was alone.

.

In his nightmares, Zuko stood at the very bottom of the world and watched the sky brighten, ink black transforming slowly to dark grey, then to blue. He closed his eyes as the first rays of sunlight pierced the horizon line, a blast of warmth hitting his face, like the embrace of an old and beloved friend.

It's time, he thought to himself, as a knife appeared in his hand. He turned to see Katara standing on the courtyard pond, dancing alone. Her face was serene, her eyes closed, a tiny smile lifting her lips. She would never see it coming.

Zuko took one step towards her, then another; she remained oblivious, occupied instead by the thousands of diamonds that swirled around her, each gem reflecting the beams of the sun at Zuko's back. She was the waterbender, and she was beautiful.

"She was, wasn't she?" came a voice, and Zuko looked over to see a man dressed in traditional Fire Nation garb, his beard neatly trimmed and his hands tucked into his sleeves.

What are you talking about? Zuko snarled quietly, careful not to disturb Katara's dance, even as the man looked over at her.

"Unne. She was beautiful," the man replied, and with a start Zuko realized where he'd seen the man before:

Roku?

"What will you do, Zuko?" Roku asked, only now it was Zuko's own voice coming out of his mouth. "What are you going to do?"

Zuko readjusted his grip on the knife. What I came here to do, he answered. He took another step, and his foot plunged into snow that came up to his thigh, pitching him forward. He dropped the knife as he fought to regain balance, and the noise punctured the quiet stillness of the morning and finally got Katara's attention.

"What's going on?" she asked, taking two steps across the surface of the pond and leaping down to stand over him, tall and graceful.

Nothing, Zuko said, but as the word echoed around him he felt the sun's warmth dip, and a chill shot through him as a shadowy figure approached Katara from behind.

"Zuko? Are you okay?" she asked softly, walking over to kneel by him. "Is it your heart?"

There was a blast of heat, and the unmistakable crackle-whoosh as flames surrounded them. The shadow loomed, tall and broad, and chuckled in a leering tone that sent shivers up and down Zuko's spine.

"Yes, Prince, what about your heart?" Ozai sneered. "More importantly, what about hers?"

Stay away from her! Zuko yelled, but it wasn't his voice; in the blink of an eye, he was now behind Katara, sneaking up on her, the fire in his veins flowing hotter and stronger than he thought imaginable. Roku lay where Zuko had been just a moment ago, looking up desperately at him.

"Please," he begged. "Please don't—"

But Zuko was already reaching out, already plunging the knife into Katara's chest, already watching the blood stain her dress the rough purple-black of a fresh bruise. He looked up into Katara's eyes, wide with shock and betrayal, and in her final moments she reached a trembling hand out and gently cupped his cheek—

.

Zuko opened his eyes slowly this time, lips already pursed, ready to slow his heartbeat, but—

Wait.

He sat up. He was still in Katara's bedroom; she had lit the lamps at some point, and now the space was bathed in rich warm light. And...and—

Zuko brought a hand to his chest. His heart was beating steadily, calmly, kindly; the details of his nightmare had faded already, leaving only a ghost of the feeling behind, and it, too, was retreating with every breath.

"Was it a good dream, this time?" Katara asked. He turned to see her on the chaise lounge again, dressed back in her casual attire; two trays of food were set on the table nearby.

"No," Zuko shook his head. "But...this time I feel different."

Katara grinned. "Good. That's really good."

He blinked. "I...yeah. It is. That's…" he looked back up at her. "Why?"

"Bending," she answered. "Now that you know I'm a waterbender, I don't have to limit myself. You've made decent progress with the healing sessions, but the ice crystals still form in between, and every time they do, they set you back just a little. So I figured, instead of waiting for them to build up and having to melt them in one session, I can just...prevent them from forming at all. See how your heart does if given a real chance to recover. Your chi, too, maybe."

Zuko swung his legs over the side of the bed and stood up, solid and unwavering. He felt stronger than he had in weeks. He felt warm , like the sun was at his back .

"Huh," was all he could say. "That's...I guess that is useful. How do you do it?"

Katara tapped the side of her head. "I just have to concentrate a little. A lot of this place is held together by the will of the last waterbender, so it's not much more work to also concentrate on you. And this way, I don't have to touch you ever again, if you don't want me to."

Zuko couldn't stop himself from smirking. "Does that mean you're thinking of me constantly?"

She mirrored his expression. "Maybe. Will you think of me in return?"

"If it means I can feel like this all the time? Sure."

It was amazing, to be able to just walk over to the table with no wobble in his knees or lightheadedness tipping him over. Zuko sat down in front of one of the bowls of stew, and Katara joined him a moment later, and for a fraction of a second it really seemed like nothing had changed at all.

Bring me the heart of the last waterbender.

Except, of course, everything had changed forever.

"So," Katara said, "have you given any thought to my request?"

What will you do, Zuko? The voice bubbled up from his subconscious, familiar and hauntingly strange all at once. A remnant from his dream, though the speaker's face was fuzzy in his mind.

What are you going to do?

Zuko didn't know who was asking, but he shuddered as he felt a phantom hand cup his cheek, like a memory of something that had never happened at all. He exhaled, smooth and slow.

She was beautiful, wasn't she?

"I can't defeat this man for you," he said softly, hiding his wince as Katara's face fell. "But...I can train you to fight back."

What will you do, Zuko? Something stupid, that's what.

It was almost worth it for the way Katara's face lit up. "Thank you," she gushed. "So much, Zuko. You have no idea how grateful I am for your help."

You say that now, he thought, ripping up his roll, unable to eat despite his stomach grumbling. But you're going to regret it later. And so will I.

He risked a glance back up at her. "So, um, I have a question," he began, feeling his cheeks get hot as he realized how tentative he sounded.

"Hit me."

"You said—earlier, when you brought me my pack. You asked me to take you along when I left this place." Zuko rubbed the back of his neck, which was an old nervous habit, and his fingers jolted ever so slightly to find that the skin back there was just as hot as his face felt.

Katara froze, spoon halfway to her lips. "Oh. Um. Yes."

"Why? If you're the waterbender, shouldn't you want to stay here?"

From the way her shoulders shrank, Zuko could tell that he had touched on something very painful. Katara's eyes lost their spark, and it was almost like watching a mask click into place. "Don't worry about it," she said, too casually. "Forget I said anything."

"But—"

"—Zuko, please, just...forget it, okay? I shouldn't have asked you. I don't want to talk about it."

He could respect that. He had to, all things considered.

"Okay," he replied. "We don't have to talk about it." If he had his way, they would avoid talking about certain topics for years, maybe forever.

Bring me the heart of the last waterbender. Every second he stayed here, Zuko was betraying Katara. He knew it, and it made him feel worse than dirt. Six years of aimless banishment were going to seem like a cakewalk by comparison.

Katara wiped her mouth with her handkerchief. "Good. And you should eat, your stew will get cold."

"Right," he said, snapping out of his reverie and turning his attention back to his food. The bowl was indeed cool to the touch; Zuko raised a spoonful of stew to his mouth and blew on it by force of habit before swallowing—"ow!"

"What? Don't tell me you broke a tooth, I soaked those sea prunes for days ."

"No," Zuko replied around the stew, "it's just hot, that's all." He swallowed, grimacing as the food burned its way down his esophagus, and Katara furrowed her brow.

"Huh, I thought I tested the temperature before I brought them up," she said. "That's strange. Must have mistimed things."

Zuko wiped his mouth on the sleeve of his robe. "It's okay," he replied. "I'm—"

Wait.

He barely managed to avoid dropping his spoon, setting it back on the table with a trembling hand as he realized what he'd just done.

"Everything okay?" Katara sounded very far away, and Zuko forced himself to nod.

"Yeah. I'm just not as hungry as I thought, I guess."

"Hmm. Well, I'll leave it for you, just in case," she said, standing up with her own tray. "I'm going to go put this away; I'll be back, and maybe we can take you to your room again?"

He nodded again, head jerking up and down mechanically as Katara left the room. As soon as the door closed behind her, Zuko jumped out of his chair, sending it clattering to the floor, and he screwed his eyes shut, hands curled into fists so tight that his arms ached.

Come on, he begged, searching deep. I felt you. I swear, I—

He stopped, one hand coming to rest on his sternum.

It was tiny, barely more than an ember, struggling to survive beneath the imposing black and cold. It was too weak to be used, probably too weak to be fed, liable to snuff out instead of catching and growing. It was hardly anything at all, and as Zuko watched, it faded almost completely away. But he swore it was there.

Tears sprang to his eyes, and he let them fall.

Inside, deep in his core, something was burning again.