His first image of her was completely warped.
The last time Zuko had seen Katara, she had been a tomboy with scruffy hair she never brushed and the same height as him with the ability to raise herself up as she treatened him with water balloons and Twinkies.
Now she was a foot shorter with hair kept back (neatly, he awed) and clothes that fit and some added mass he'd never managed to notice before.
It was like staring at a carnival mirror of her, and it looked good.
She hadn't noticed him yet. She still wore blue like she belonged in the sea, and he wondered how he was going to approach her, or if she would even recognize him, or remember him, or maybe he could just pretend he hadn't seen her and didn't know it was her, because if she didn't recognize him, it'd be ten times worse.
Then she turned around.
She turned around, saw him, and there was the obvious look of shock and surprise.
She was never going to forget that scar, or the first time she saw him with it, or how she could say nothing towards it, because she knew what it was like to lose a mother, but not what it was like to carry the burden of her death so obviously.
She choked out his name. It was like a broken yelp.
He swallowed, not knowing what to do. At all. "Katara," he breathed. "Hi."
She stared. "Hi."
Now what?
It was like he'd stepped into a dream. A dream he almost wished he wasn't having because oh my god this was awkard.
And they were in front of the entire class, which did not help their situation.
Katara cleared her throat, reading his mind. "Let's, uh, sit down."
So they did. Right beside him was a girl he hadn't seen in four years. Were they still friends? Were they still the same people? Or had life torn them apart with more than just miles?
"You're here," Katara whispered as class began, and he barely caught it. And a smile began breaking over her face as she stared at him, and he couldn't help but smile back.

---
It wasn't until after they got out of the classroom that she grabbed him in a hug, nearly knocking him over.
"I can't believe you're here!" she squealed. "I thought I'd never see you again!"
He grinned (it was something he hadn't experienced in a long time) and wormed out of her grip. He was still unsure what to say, because this was Katara, and he didn't know if he was prepared to deal with the outright Katara-ness he hadn't experienced in oh-so long.
It was time to get caught up.