Even waterbenders need to breathe.
Katara broke the surface with a gasp: she'd been submerged for almost a minute after all. There had been a moment back there when she'd wondered if she'd make it to the end of the particularly long tunnel, but she had trusted him and it had paid off. Where she was, exactly, she wasn't sure. Some kind of air pocket, she assumed, like the one she had just left.
The (thankfully) extinct volcano was riddled with tunnels, most of them flooded. Sooner or later they all seemed to spill back into the lake, as Katara had discovered over the course of the afternoon. This was the only one that so far appeared to be breaking that pattern. Though it surely meant a long journey back, the deeper she swum into the bowels of the volcano the more excited she became, half expecting to stumble across some lost treasure or the remains of an ancient civilization. Or something silly like that, anyway.
The only source of light was a faint blue glow from beneath her. Katara looked up, squinting into the darkness, but was unable to make anything out.
A splash beside her announced the arrival of the tunnel's discoverer. Like her, he was quite out breath.
"Katara?" he spluttered.
"I'm here!" she replied, moving towards the sound of his voice.
"Oh, good," he said. "Thanks for waiting!"
She titled her head curiously. "You're the one who is supposed to be showing me the tunnels, why do you always follow me?"
"You'll see," he said mysteriously. "So what do you think?"
"Think?" echoed Katara. "Of what?"
"Well, this is the place I told you about."
"Really?" Katara's interest peaked. "I'm sorry Aang, but I can't see a thing- Oh!" While paddling about in the pitch black she'd failed to calculate the risk that she might, at one point, bump into her companion. Which, naturally, she did. "Sorry!"
Aang chuckled. "It's okay. At least we each know where the other is now, huh!"
Katara agreed, if not a little bashfully.
"Right," continued Aang excitedly. "So what do you know about ice?"
Katara grinned. "I'm from the South Pole, remember?" She nudged his shoulder playfully. "I bet I know a lot more about it than you do!"
He nudged her back. "Fair enough, but I should have been more specific. What do you know about ice and light?"
She thought for a moment, wondering where this was going. "Well," she began. "Ice refracts light, kind of like-"
"A crystal," interjected Aang. Katara nodded.
"Yes, just like a crystal. You'll end up projecting every colour of the rainbow. If it's a smooth surface it reflects the light instead, exactly like-"
"Like a mirror!"
She giggled. "Hey, I thought you were asking me!"
"Sorry."
"Light is reflected on a smooth icy surface like a mirror, and it if it's in a crystalized form then like anything else transparent and crystalized, ice refracts the light. Is that what you wanted to know?"
"Yes," murmured Aang. "Exactly."
"But you already seemed to know that, so why ask me?" Katara thought she caught a pale flash of teeth in the darkness.
"You first asked me why I swum after you and not before you," he said in an assuming tone. Katara smiled: it sounded very similar to Sokka's detective voice. "Now," he continued. "If you will, Miss Katara Water Tribe, dive underwater for a moment and look back down the tunnel…"
Katara did as she was told.
When she resurfaced it was again with a gasp, but this time one of surprise. "It's all frozen!" she said. "Like a zig-zag, what-" Her eyes widened. "Mirrors?"
Another glimpse of teeth. If she could see him properly, Katara assumed that Aang would be grinning ear to ear.
"Did you know," he said lightly. "That crystals form in volcanoes?"
Katara laughed as everything fell into place.
"Clever," she said. "Very clever, Mr. Avatar." Aang chuckled along with her, and then quite suddenly his voice was in her ear.
"We just need one more mirror for it to work." The words had barely registered when Katara felt a sudden chill about her toes as the water somewhere below them turned to a perfect, smooth disc. A soft blue radiance lit the chamber. And then, they were consumed by colour.
Off of every surface glittered a thousand different tones, some of which Katara had never seen before. It was like being inside of a diamond at the precise moment when it was struck by the sun. As she circled in the water, trying to take it all in, the ripples contorted the reflected light from the mirror below: the rainbow lights danced.
"Do you like it?"
She tore her eyes from the spectacle and fixed her gaze on another. The bright beams that drifted across the boy's face seemed to make him glow. He smiled, and a flash of blue twinkled in his eyes for a moment before being replaced by a different colour almost instantly. Katara couldn't bring herself to blink.
"It's incredible," she said breathlessly. "It's like the Cave of Two-" she stopped. Aang's face has just lit up with the most spectacular colour of all: bright red, and it had nothing to do with refracted light.
"That's what I thought," he said quietly. "And that's why… I thought you'd like it."
Katara smiled, feeling her own cheeks flare.
A moment of silence was shared as they mutually enjoyed the lights. Aang felt the back of his neck prickle, and he turned to find Katara watching him, wearing an odd expression. His eyes didn't leave her face as she moved across the pool towards him. He inhaled sharply as she raised a hand to cup his cheek, shivering as her fingertips trailed down his jaw. The wall of the tunnel was suddenly against his back. Underwater, his fingers curled against the winking crystals.
She was very close.
Katara's eyes fluttered to a close, and Aang swallowed hard as she gently pressed her forehead to his. For a long moment he was content to simply soak in her features, listen to her slow, even breathing and enjoy the sensation of the silky ends of her hair lazily curling against his bare skin in the water.
Ordinarily, his mind would have been screaming success, but for the time that Aang and Katara remained close together surrounded by sparkling lights in an air pocket under a volcano, nothing registered but the five senses. They swamped all brain functions, stirring up a warm, fuzzy feeling that filled him from tip to toe.
He forgot about the warm water rapidly melting the ice, he forgot about the long swim back to the lake. He forgot about Sokka, presumably having long given up on trying to get Toph near water, and about Appa and Momo fast asleep on the black rock. He forgot about having to check his Fire Nation disguise twice over to detect any arrows betraying his person when they eventually left the lake. He forgot indeed that they were in the Fire Nation, and about the invasion plan. He forgot all about the war, the Firelord, Zuko and Azula. For a split second, he forgot about the genocide of his people and the mammoth responsibilities he would carry for the rest of his life. Just for now, he was alone in a cave filled with sparkling rainbow crystals with someone who outshone them all.
As they remained against the wall in the gradually dimming light, Katara's hand still ghosting over his face, a mutual feeling of understanding passed between the two. Despite the fleeting kisses, the hugs, the hours spent in each other's company, the sweet gestures and the wild dances, only now did things seem, quite suddenly, different. Perhaps friendship wouldn't be enough to define Aang and Katara anymore. Aang smiled at the thought.
Katara opened her eyes, and met his.
Her fingers trailed around to the back of his neck, combing the short strands of dark hair that Aang was suddenly very glad to have. She drew a soft breath (he felt the air trickle past his newly exposed cheek), tilted her head and leaned in closer.
Aang's stomach did a somersault. Thudding like a sledgehammer trying to beat its way out of his chest was his heart, beating faster than he dared to count. His ears barely caught the soft splash as his hands settled upon her waist.
Nothing happened.
Aang looked up the moment he detected a change in her breathing. He whispered her name. As if she'd been struck by lightning, Katara suddenly jerked backwards out of his light grip with a splash, her eyes wide and her lips half parted. His brow creased in puzzlement.
"Katara?" he asked softly.
But the light was rapidly fading. The crystals grew dimmer and the colours faded away. The last thing Aang saw before the little cave was enveloped in darkness once again was a glint of uncertainty in Katara's eyes.
"Katara?" he called, louder.
She answered, saying something about meeting him back at the lake in an unusually high voice. Then, a loud splash, and she was gone.
Aang grimaced, whirling about and whacking his head on the wall a few times for good measure. It looked like it would take at least one more cave before he would get it right.