This is a much longer version of my drabble by the same name.
In person, Zuko was quieter than she ever imagined he'd be. Whether it was his nature or his grief was a question Katara couldn't answer, but she found herself believing that whichever it had once been was irrelevent; silence had become his nature.
It was not that Zuko refused to speak or that he was any more able to rise above Sokka's daily jabs than the rest of them; it was simply the fact that he never started conversations. Left to his own, with no outside pressure demanding communication, any request that couldn't be given in gesture was meted out in brief, functional statements that displayed as little personal inclination toward talking as could be displayed without being downright rude (also surprisingly, Zuko was rarely downright rude, although remembering how he'd behaved with his uncle, Katara suspected this was not a positive sign.) If battle was to be had or a problem in the group to be solved then Zuko was as vocal as herself or Toph, often more so, tossing instructions about as if Appa were his ship and they merely his soldiers. But when the threat was gone and all were back to being just people again instead of warriors and avatars, Zuko's will for interaction went out like a candle.
The boy was not, Katara had decided, a people person. But his heated opinions on tactics and bending contradicted so starkly with his mute-like behavior in everything else that she felt sure Zuko's silent nature was not something he was born to. So one evening when it was just the two of them by the campfire Katara posed the question, because being direct was the only way to get anything useful out of Zuko.
"Back on your ship,"—even directness was not a guarantee, but she'd found him utterly oblivious to subtlety—"were you always this quiet when you weren't ordering everyone around?"
"Being around the same people for three years means you quickly lose things to talk about," he replied, "and my uncle talked enough for the both of us."
A few weeks ago this reference to the dead would have sent Katara scurrying, but in the middle of Aang and Azula's last skirmish she'd decided friends fight together better than mutual travelers, and now that she'd decided to become Zuko's friend Katara was no longer willing to wait for him to open up first.
"Well, what about when you were younger? Were you a quiet kid too?"
The corners of Zuko's mouth creased downward. "I learned to speak, I learned when not to speak, I learned to fight with Azula every time I felt like speaking. That should explain enough."
"So you were a quiet kid," Katara murmered, guessing by his cryptic response and what she knew of Azula that the prince must've avoided a fight with his harpy sister whenever possible.
"No," Zuko said, standing up and walking away from the fire. "I wasn't."
Zuko stomped through the bushes in the direction of the creek, every once in a while peeking over his shoulder. Not a dozen feet behind him Katara followed, spheres of water bouncing back and forth in her hands. Every time he checked she was there, and every time he forced himself not to look he could still hear her footfalls. Even since he'd left the campfire to walk by himself in the slowly fading light she'd been following him without bothering to pretend otherwise. Finally he spun around and bit out a question.
"Why are you following me?"
Katara half-smiled and combined all her water into a single sphere which floated gently above one shoulder. "I wanted to apologize," she replied, "for upsetting you with my questions."
Zuko's head tilted back a fraction, and he examined her face appraisingly. "You're not sorry for asking me questions," he said in a voice as flat as it always was these days. "You wanted to invade my privacy earlier. So why are you really following me?"
The waterbender's friendly smile tumbled into a delicate frown. "I wasn't trying to invade your privacy, I just wanted to know more about you."
Zuko crossed his arms and waited.
"Okay, okay!" Katara burst out, waving her arms and walking forward a touch sullenly. "So I guess that is invading your privacy. Fine! You're right, I'm being nosy. But I really didn't mean to upset you, you know. You're too sensitive."
He shook his head and said dully, "I'm not upset. I really don't care."
"Yeah I know, you don't care about anything these days," Katara muttered, but not low enough to escape being heard. She looked up guitily; now Zuko was beginning scowl.
"I care about things, Waterbender."
"But you don't care about yourself? You care about 'things' but it doesn't bother you at all if I ask about your past?"
"Whether I don't care about myself or whether I'm overly sensitive, I don't see it as any business of yours." Katara felt a flush of early victory; she had struck a nerve. His tone was still even but his expression said she was getting to him. Annoyance was progress at this point, if it got him to react.
"It is my business, Zuko. I'm trying to be your friend."
"I don't need you to be my friend."
"Someone needs to be."
Calmly, "Why do you think you have the right to decide what I need, Katara?"
He was receding again, growing more distant with every successive sentence as annoyance buckled under the armor of apathy. Now he'd turned the conversation back on her. But that was okay; Katara could work with that.
"Alright then, fine. I need you to be my friend."
It was the wrong thing to say. Zuko rolled his eyes and started walking away. "Wait!" she yelped, and caught up next to him, stepping faster than normal to keep up with his longer stride, since he certainly wasn't going to slow down on her account.
"I mean it, Zuko. I always need more friends." Zuko said nothing, and Katara winced as she heard herself. "Sorry, that didn't come out right either. I just think that we should be friends, since we're traveling together now. We trust you, but we don't know you."
Zuko burst through the underbrush to stand on the edge of a small cliff half a dozen feet above the creekbed. He threw himself into a sitting position in a far from prince-like manner; combined with the eyeroll it was the most childish behavior she'd seen from him in days. Katara sat down next to him, sending her water sphere back into her canteen. If she were to need it the creek would provide.
"If you trust me," he asked though Zuko did not turn to look at her as he spoke, "why is it so important you know this stuff about me? You know everything you need to know: I was a prince, I'm an exiled fugitive, I'm not chasing you anymore, I want the war to end as much as you do. That's all you need to care about. It's all I care about."
Katara folded her hands in her lap, staring down at them. She took a moment to gather her thoughts before speaking. "I suppose it's like the difference between just surviving, and actually living. You have to have something with you right now to fight for, not just the idea of the future. For us, that's family and friendship. I want to be your friend. I can't say about Sokka, but Toph likes you, and you know Aang has wanted to count you a friend for longer than any of us."
Zuko picked up a pebble and flipped it into the creek. "Toph is a brat," he dismissed, "and Aang tries to make friends far too easily."
Katara glared at the apparent snub, then surprised them both by laughing. "You're right," she beamed, watching Zuko's next pebble bounce along the stones below and into the shallow water of the rockbed. "He really does."
"That's why we're with him, Zuko," she said, finding new strength in her words as she thought of the Avatar's ability to effortlessly gather people to him. "And that's why it matters that you're our friend and not just another pair of hands for bending. It takes more than just fighting on the same side to make a difference. It takes—"
Katara's words jammed in her throat as Zuko turned toward her and she abruptly got a double blast of sight and scent: Zuko and she were sitting much nearer than Katara had realized, and now that they were turned toward one another his face was less than a foot from hers, the closest they'd ever been. Suddenly the smell of him overwhelmed her senses; the oak and eucalyptus of the surrounding trees clung to his shirt, overlaying but not completely hiding the sweet, cloying perfume of smoke. Was it smoke from the campfire, or from his firebending? She'd never thought he might smell like anything, but now—
"Katara, it takes what?"
He was talking to her. More importantly, he'd actually been listening. What was she talking about?
Right! Friendship. Aang. Loyalty and the greater good and stuff.
"Sorry, Zuko, I just, for a second..."
"You what?" He was still sitting so close to her. How had they ended up here?
"...Nevermind. What I meant to say was that we can't fight side by side if we don't become a real team. And that takes more than just trusting you not to kill us. It takes true friendship, relying on each other, and knowing what makes each other tick."
The question popped out of Zuko so quickly and so softly Katara wasn't sure she heard it.
"What makes you tick?"
"It's nothing!" he said quickly, and was on his feet in less than a breath. "Getting dark," he observed.
Katara looked around, then up at the sky. "Yeah," she agreed, still a little confused at his sudden departure. "We... we ought to get back. Sokka and Aang might've already started cooking."
Zuko was already several feet ahead of her, but she heard his derisive snort. Katara watched his back as they walked and felt a nervous, slightly giddy smile overtake her.