"It was like bloodbending," said Aang, with a shrug. "What I did with Ozai. Not that I have much experience with it."
"You could get some," said Katara, putting enough emphasis on the last two words that Zuko figured it was a conversation they had had multiple times in the past. "I don't understand why you'd think it's a good idea for the Avatar to voluntarily stop himself from learning as much as he could about every possible type of bending-"
Aang replied, and Katara argued further, and Zuko watched them fight, biting his lip. They'd been here - in his home, in the Fire Nation - for months, the two of them, and he'd been with them for much longer than that, but he still didn't really feel like it was his place to interject in their arguments. Or even in their conversations, at times.
"I guess I just don't see the point-" Aang was saying.
"The point? You just said you ended the war with it," Katara interrupted.
"Well, it's not like I'm going to have to take bending away from the current Fire Lord," Aang said, and he threw a wink Zuko's way. Zuko smiled in response.
"You're just afraid," said Katara, throwing her hands up.
"Of course I am!" Aang replied, like it was obvious. "We're talking about controlling people who wouldn't be able to fight back. It just seems like too big a weapon."
"And what are you going to do if someone else decides to use that big weapon against you?"
"They couldn't," said Aang, looking a little taken aback.
"Oh, of course," said Katara, her tone clearly saying what she thought of this naivete. "I still think you should practice, just in case. Something small, just try to make my arm move-"
"No!" said Aang, alarmed. "What if I hurt you?"
"You won't," said Katara, rolling her eyes. "Zuko?" she asked, and Zuko froze, hoping he wouldn't have to share his opinion.
"I don't want to hurt him, either!" said Aang, sounding a little shrill.
Katara ignored him. "Can I try it on you?" she asked, looking straight into Zuko's eyes. She looked serious, like the question meant more than the casualness her tone implied.
He held his breath for a second, losing himself in her gaze, and he was reminded of jumping in front of Azula's lightning for her, of rolling around in the dirt to save her from a falling temple- "Yes," he said, simply. It hadn't even been a question.
He felt a prickling sensation rushing in his veins - literally in his veins, he realised, a little hysterically. It was like something infinitesimal was just a little bit wrong, like his blood was moving half a second out of step with the rhythm his heart beat. It was hot and cold at the same time and it was like Katara's hands were rushing all over his body, but the inside of his body, and-
His arm raised slowly. And then he waved. Dorkily.
He laughed, a short, disbelieving laugh.
"Does it hurt?" Katara asked him.
"No," he said, though he suspected she knew. "It's weird, but it doesn't hurt."
Aang walked closer to him. He was looking at Zuko's arm, like he expected it to explode any minute. He paused. Then he turned his head towards Katara.
"You have his entire body at your disposal, and you go for a wave?" Aang asked. There was a cheek in his tone that threw Zuko off-kilter. It sometimes felt like Aang had sped through his entire adolescence in the months he'd spent here - working hard to rebuild the Fire Nation and reestablish its place in a peaceful world, yeah, but also finally free from the burden of the world pressing down on his shoulders. He had shot up in height - Zuko didn't even have to angle down to look into his eyes - and there was an undercurrent of heat in his interactions with Katara that made it pretty clear that he'd grown up in other ways, too.
"What, did you want me to undress him?" asked Katara, who looked much more at ease with the flirty tone. She raised an eyebrow and looked at Zuko, like she was pretending to consider it-
And Zuko felt his blood move on its own again, but in a much more familiar way. In the way it did sometimes when he sparred with Katara - when he caught Aang kissing her - when either of them laughed. He dropped his eyes, hoping to hide, but she had just been inside his blood, and he felt pretty sure she was still hyper-aware of all of its movements.
Zuko threw off a fireball in the air, just to give himself countenance. Katara smirked at first, like she was on to him, but then her eyes got wide and she said - "Wait, do that again."
"What?" Zuko said, dumbly.
"Bending," she said.
And so he did. His blood got the prickly sensation again as his arms went through the familiar motions, and he knew what she was after. He went as slowly as he could, exaggerating the movements like he had when he taught Aang. "Stop," she said, finally. He held his breath. Aang's eyes were going from him to Katara and back, like he knew what was happening but didn't dare intervene.
And then his arms moved again. Did a good approximation of his earlier routine. He felt the usual heat passing through him, combined with the cold of Katara's bloodbending, and then- fire burst out of his fingertips.
It resembled the feeble fire that had been all that got out of him when he was a kid, rather than the more imposing flames he had been used to recently. But it was fire.
"Hah!" Katara laughed, delightedly. "Can I try again?"
"Yes," he smiled at her, fondly. "Try it a little more like-" he said, miming a refinement, feeling her presence inside of him.
He shot a fireball in the air. Or she did.
"Wait," she said again, her eyes bright, her hands stretched out, and Zuko could almost see the power crackling out of them. She looked happy, and excited, and he wanted to kiss her so badly it hurt.
She turned a hand towards Aang. "Can I?" she asked, and Zuko wondered what he was going to say, after he had just went on about the dangers of it-
"You know you can," Aang said, instead, like it went without saying. Zuko felt something familiar wrapping around his heart and tightening - the pressure as strong as the bond between the two of them.
Zuko felt the pricklings of cold leave his body, and he felt strangely empty, all alone in his own body. Aang started moving, movements Zuko had seen him do previously, but without his usual grace. Katara didn't have to ask him to show her an example of his bending - she had seen him go through the motions enough times. In all those months they were together, while Zuko was against them, wasting so much of the time he could have had with them.
Zuko felt a breeze, and Aang moved his fingers a little. "Like that," he said, relaxing his hand, and Katara bit her lip in concentration, and then, Aang was flying.
Katara laughed again, and Aang did, too, despite himself. He was hovering, only a couple of inches above the ground, bobbing up and down uncertainly. He was looking down at Katara like she hung the moon.
Then Katara frowned, and Zuko felt the ground rise up underneath him. And he was throwing a fireball again, and it was suddenly raining, and-
"I'm the Avatar," said Katara, delighted.
She only lasted a couple of seconds, and she seemed exhausted as Aang dropped down softly, and the ground under Zuko slid back in its place, bringing them both close to her. She smiled.
"Well, you still have a lot to learn-" said Aang, a little huffily.
But Zuko just smiled. "Maybe, but I believe Katara can save the world."