The room was dark when Nise entered. She wasn't surprised. Akui had never been one to light himself up.

With a small fire burning in her hand, she strode into the center of the room, and looked around her. When there was no reaction, she spoke. "You can no longer hide in shadow."

A voice answered from the darkness. "We don't have to fight."

With a smirk, Nise pinpointed the voice and readied herself. "Yes. We do."

"I'm not evil! You know that!"

"You host Vaatu. I'm sorry brother, but this must be done."

There was a woosh as Nise summoned a gust of air and threw it at her brother.

Akui crashed through the wall and slammed into the walkway outside.

As he scrambled to his feet, several shards of ice were flung through the ragged opening at him.

Staggering, with blood flowing from several gashes, Akui managed to redirect the ice at the last moment, narrowly avoiding impalement.

Covering his wounds in healing water, trying to ignore the shouts from the civilians clustered at the edges of his vision, Akui focused on the opening he had recently been thrown through, searching for motion in the shadows. "Nise!" He shouted. "Stop this madness! I'm your brother!"

His answer was a torrent of water that slammed into him, forcing him across the street and into the wall there.

As Akui slowly got to his feet, Nise stepped through the opening.

There were exultant shouts from the crowd. "The Avatar!" "It's her!" "Go Avatar Nise!"

Nise acknowledged the cheers with a wave of her hand, then focused on her brother again, dropping into a combat stance and raising a giant orb of water over her head. "It's over Vaatu. Surrender!"

Akui moved until his back was to the the wall. "Nise, please. It's me. I'm your brother! How can you do this to me?!"

Nise shook her head. "You are no brother of mine, Vaatu. If you will not surrender willingly, then I will make you." With that, Nise unleashed a river of water at her twin.

Akui stood his ground. As the water rushed at him, he bent it around him, curving it away and forcing it to sink into the ground. "Sister, please, I do not want to fight you!"

With a few short moves, Nise unearthed the water and sent it back at her brother. "Then surrender brother. The time for words is over!"

Acting reflexively, Akui bent the water away once move, sending it straight at his sister.

Nise raised a wall of earth in front of her, absorbing the brunt of the attack, while she rolled clear and launched a series of fireballs at Akui that forced him to create a water shield to protect himself. "Well, brother, it seems you've shown your true colors at last. It looks like this little encounter may not be boring after all."

Nise went on the attack, using water jets with the occasional fireball and boulder to keep Akui off-balance.

In the face of this devastating assault, Akui was slowly forced down the street towards the waiting police, barely able to hold off his sister's attack.

With him within range, and distracted with his sister, the police acted.

The first warning Akui had was a hissing whistle, then cables wrapped around his arms and electrified.

Akui screamed at the unexpected shock, before slumping forward onto the ground, barely conscious of the officers grabbing his arms and hauling him upright, or of his sister's approach. But he heard her words to him.

"Sorry brother." She said, fashioning a spike out of ice. "I wish there was another way. But harmonic convergence is in just a few hours, and I can't risk Vaatu escaping before then."

Akui looked up at his sister, grief and horror on his face, as Nise brought the spear down.

It never reached its mark.

A burst of wind erupted from Akui, knocking his sister and the police away.

Bystanders stared as Akui rose into the air on a tornado of air, head lowered.

As his sister and the officers got to their feet, Akui's head snapped up and he locked gazes with his sister, drawing gasps of shock from the onlookers.

Akui's eyes were glowing with Avatar power. But rather than the orange of Vaatu, his eyes were the white of Raava.

In silence, all eyes were drawn to Nise, standing staring up at her twin.

Whispers echoed through the crowd. "What's going on?" "How is that possible?" "It's a trick." "Does that mean that she's..."

The murmur was cut off by Akui. "Deceiver." He accused.

Nise shrugged, a smirk growing on her face. "I see no point in denying it. I was starting to wonder what had happened to you, Raava. Well then, let us meet once more in battle, but this time I shall be the victor."

Nise's eyes took on an orange glow, erasing any lingering doubts as to which spirit she represented. Rising into the air on a tower of water, she continued her monologue. "It was so easy, you know. Siphoning the elements from you while I reformed, disrupting your Avatar, impersonating you. Humans truly are fools. Perhaps once I vanquish you, I will keep a few around for my own amusement."

Akui's eyes dimmed, returning to normal. "Sister, please, listen to me. You don't have to do this. You can fight him."

Nise laughed. "You have no sister. Before you were born, I took her over, rewrote her from the inside. For my purposes, I became your sister. Without me, she is nothing."

Shock and horror warred on Akui's face. "No. Please."

Nise laughed. "You are hopeless Raava. One shock and your Avatar falls apart. This battle will be no challenge."

Akui closed his eyes for a long moment, shoulders heaving with silent sobs that he slowly got under control.

Nise smirked. "What is this Raava? Is our battle to be over so soon? A pity. I was looking forward to it."

Akui's eyes snapped open, glowing white. "No. This is not over." He straightened up and readied himself for battle. "You will taste defeat thisday, for my sister, whose life you stole."

Nise flashed a predatory grin. "Enough words."

The Avatars launched their attacks.

The battle began.