They had already known each other many years- But, that isn't important to our story- this isn't about those years.
This is about the ten days it took for them to fall in love.

On the first day, she arrived.

A sea of unfamiliarity, blue and cold hands and smiles, she was. Lady Ambassador of the Southern Water Tribe, she was. Overwhelmed by how beautiful 16 going on 17, he was.

Curious- she thought. How did the Fire Lord learn how to be so appealing? She assumed it was her boat-to-land sickness.

On the second day, he wandered about.

He signed some papers. He ate some lunch. He drank some tea. He thought about how he'd missed her laughter. She slept. She ate. She got butterflies when he passed her in the halls.

She assumed it was still her boat-to-land sickness.

On the third day, she went to the doctor.

"No, Miss Katara," the doctor said, "you're fine." She left in a panic. I have boat sickness. I have to have boat sickness. Zuko stopped her as she left the doctor. "Are you alright?" He let his hands gently slip around her waist.

She practically threw up on his shoes.

On the fourth day, Zuko recieved a note.

Have boating sickness when you walk by. Could you please not pass me by anymore? Thanks, Katara.

He made a point to pass her by. As he did, he brushed her hand gently, and smiled. This time, she just felt happy. No nausea. Was happiness a symptom of boat-to-land sickness?

She hoped so.

On the fifth day, they had a grand dinner.

"Are you cured?" he asked, offering his hand. (which was sticky with nervous sweat, oops)

"Possibly," she answered.

"Will you dance with me?" he asked.

"Only if you wipe your sweaty hands."

On the sixth day, he knew he was in love with her.

He stared at her during breakfast. He daydreamed during tea. He turned red when she brushed his shoulder with her delicate fingers. She asked him if he had been on a boat recently. "Katara, a boat?" he asked, smiling weirdly.

She told the doctor the disease might have been contagious.

On the seventh day, she admitted she wasn't sick.

Toph asked her why she was acting so strange. "Ever since they danced," she murmured, "he's been like a lovesick bastard." When Toph told Katara that, she laughed. And laughed some more. Then had a realization and turned beet red and told Toph not to say anything.

On the eighth day, everyone was silent but Sokka.

Toph knew. Aang (damn that Fire Lord, for being older and well muscled) knew. Sokka asked, "Why is everybody so quiet? Is there something I should know?"

Katara and Zuko choked simultaneously.

On the ninth day, Zuko told her.

"What?! Zuko, you're crazy." She exclaimed.

"Maybe so," he replied, "but you like me too."

She huffed. "Prove it," she snapped.

So, he tried to kiss her- she let him. She paused afterwards, and put a hand to her mouth. "Okay then."

On the tenth day, she left for her home. For how long, he didn't know. He kissed her goodbye, quietly, and let her go.

She came back twenty minutes later- she "wasn't one for boat sickness." And they lived happily ever after.