A/N: Here it is, part two of what began on Day 06: "Power Couple", to be continued on Day 16: "Intimacy". I hope I managed to portray the Final Agni Kai well, as it wad my first time writing an action/combat sequence, and I kind of just described what happened. Some stuff may be out of order or incorrect because I couldn't be try hands on proper footage because I forgot I AtlA is on Netflix where I live and Youtube only is so good. But I, anyways, decided to write down most of what happens, plus some stuff I added myself, and a small, hopefully meaningful line about Azula.
Disclaimer: All rights go to Bryke and Nickelodeon.

The battle of siblings was as ferocious, as it was beautiful. Katara could not help but marvel at the tendrils of flame shooting from the royals' hands and, at times, feet. The way the flames swept across the courtyard, and the way Zuko skillfully deflected his sister's angry blue flames.

"What's the matter? No lightning today?" He taunted her. Katara silently prayed he knew what he was doing.

"Afraid I'll redirect it?"

Azula cackled.

"I'll show you lightning!"

As Zuko steadied himself, standing calmly and groundedly, she swirled her arms around, sparks at her fingertips. The mad princess was just about to strike and- Azula's gaze swept over to Katara. A cunning smirk crept over her lips. The firebender growled, and sent her lightning towards Katara.

"No!"

Time slowed as she herself froze in terror.
She saw Zuko race sideways, jumping into the path of the lightning- and crash to the ground before her, the lightning around him in his fall, saw him spasming and twisting from the electricity as Azula laughed and stumbled towards her.
Losing all rationality, Katara rushed towards the ex-prince, coating her hand in water, already reaching out to the one who meant so much to her. But in her unhinged state, Azula would not let her. A jet of fire shot towards Katara, who barely deflected it. Azula leapt into the air, sending another torrent of blue fire in Katara's direction, narrowly missing Zuko on the ground, reaching out to Katara like a sailor for a lifeline.
The azure flames separated them as she jump-rolled out of harm's way, heat licking at her heels. She turned around to the image of Azula boosting herself up into the air, landing on the roof and sending a shot of fire at the waterbender, who saved herself by running behind one of the columns at the edge of the courtyard, getting it charred in the process. A bolt of lightning was sent her way. She ran out of hiding, gathering the Water from the basins in her wake, surfing across the courtyard on them as Azula rocketed across it on her flames, sending more and and more after Katara with every attack. In a last ditch effort, having frozen up all the water in the basins, Katara hid in the row of columns again, panting.
Katara scanned her surroundings. With Azula so powered up by the comet, she stood little chance of beating her with just her bending, given her limited supply of-...Water. Her gaze stopped at the grates in the ground. She sensed water flowing underneath them. She found a sturdy chain not far off. A plan formed in her head.
Azula prowled closer and closer to her, taunting her as she neared. When she wa close enough, Katara struck, sending out tendrils of water to attack the unhinged princess. Azula laughed and basically ignored them. Desperately, Katara took a deep breath, and brought up a large wave of water from the drainage below, encasing her and the princess in it, Katara freezing it instantaneously.
Releasing that breath deeply through the nose, Katara began "swimming" through the ice, tying the princess up with the chain she'd grabbed beforehand.
She dropped the ice as soon as she'd finished, not wasting even a second to go to Zuko.
With tears in her eyes, she rolled him over onto his back, and gloved her hands in water, placing them on his torso to heal the already forming scar, praying to the spirits to let him live - please, just let him live! - as his sister writhed and howled in her chains, spewing fire and fury.

"Thank you," he crowned hoarsely, squeezinging her hand before he pushed himself up, supporting himself on his elbows. She smiled down at him, and in a spur of the moment-type feeling, tilted his chin upwards and kissed him. It wasn't anything deep or passionate, but that didn't make it any less special to her - he was her saviour, her opposite, her equal, her partner, and maybe even, her soulmate.
When she broke the kiss, she found him gazing at her wonderingly, his hand reaching out to her almost yearningly.

"No," she told him gently, helping him up, marvelling at his stunned expression,"it should be me who is thanking you, Zuko. You took lightning for me. That's more than I could ever do for you."

At the edge of the courtyard, they heard Azula scream something. They turned towards her. Neither of them with hatred or spite in their gaze - only pity for a fallen warrior, and a broken girl.