Calor
She ducked out of the way, her brown hair swinging behind her. He sent a stream of fireballs at her head, and she rolled on the pavement, her legs moving rapidly to keep up. She swiped a barrel of water at him and he evaporated it, making it harder to breathe.
The Fire Lord's private training arena was located underground, in a room with no windows, just cement walls. They were a small amount of water barrels left, and Katara was using them wisely and sparingly.
She threw a long and very sharp whip towards him and he dove for her, yet it still sliced him across the back and he hissed.
He sent a stream of fire at the ground, heating the cement, making it more difficult for her to slide across a pathway of ice. She attempted to, but it melted almost immediately, sending her flying into the concrete, scrapes and burns erupting on her knees and elbows.
She made for his ankles as he regained his balance, sending him crashing onto the ground, her hands going to grip his wrists to the floor, legs on either side of him.
She leaned in, "I win."
They both seemed to realize how close they were at the same time. They were both panting hard from exertion, breaths mingling together. Their bodies were laden with sweat. He parted his lips to say something and-
He was on top of her now, holding down her wrists.
"Nope, I win," he chuckled.
Their lips seemed to mold together in an instant, her hands going to his broad shoulders, his to her legs. She seemed to sigh his name and he let out a breathy moan, and both of them tightening their hold on each other.
Minutes later, a loud knock interrupts them and they jump away from each other, Zuko literally leaping off of her and they both turn towards the door.
It's a servant, informing them that the Fire Lord's presence is being requested. The Fire Lord dismisses the person and helps Katara up.
"I'll see you later?" he asks, as he seeks her eyes for reassurance. She nods, a wide smile on her face, and kisses him quickly, before walking rapidly to her room without turning back.
Once she enters her room, she whispers, "Tui and La, that was so hot."