Author's Note: So much big news this week: Korrasami comics confirmed, first close-up images of Pluto, and the sad passing of Satoru Iwata (the CEO of Nintendo). In order: Yay, yay, and boo.

Thanks as ever to my beta, Raijin Tora.

Unspoken Words

Book Three: Answer

Chapter 10: Equivalence

Teaser: The final showdown with the Eternal, and the truth of its plans is finally revealed.

I fall for a moment, but I quickly manage to find my feet. Where am I? What had happened?

It takes a bit, but I find myself again. The last thing I remember is Asami electrocuting me with her glove, and then consciousness faded from me. And then I saw… something. A vision of some sort. Possibly two visions.

Perhaps it was something like a dream, my mind going haywire for a moment as I was knocked out. That seemed likely.

As my mind reaches the present, I look around. Nothing but darkness surrounds me at first. After a few seconds, a white circle grows out from my feet, as if outlining a platform I'm standing upon. Once it reaches its maximum size, twelve marks appear along the outer edge, and two large beams of light stretch out beneath me.

A clock face. I've been here before, in the Tree of Time, when I saw my first vision from Avatar Varina's life. So I'm not simply unconscious and dreaming then. At least, I might not be.

I turn upward, finding a furious red star having appeared in the sky above me. The spirit who resided in the Tree of Time, most likely. But why was it here? Or was it… "Are you… the Eternal?" I say.

The red orb is silent for a moment, but then it speaks, pulsing with each word. "I am not," it says. "I understand why you might think so, Avatar Korra. Rest assured, we share a common foe in the Eternal."

I narrow my eyes as I look at the star. I'd only ever contacted this spirit while in the Tree of Time, and I'm pretty sure Varina had never contacted it elsewhere either. "Then what are you doing here? This isn't your tree," I say, still not entirely sure this was indeed the same spirit. But for now, I would trust it.

"The Tree of Time is my home," the spirit says, "but that does not mean I cannot leave it. I came here with your friend, Asami Sato, so that I might ensure that the Eternal's plan could be stopped. She has been successful so far."

I nod slowly. "Yeah. She has been. It should be over now, though, right? If the Eternal can't use me to fight against Asami, there's really nothing left to get in her way."

"That is correct," the spirit says. "She is free to act as she believes best. It is not yet guaranteed, however, that what she believes to be best will actually be so. Humans never fully know what the future might bring, and I am certain that the Eternal will try to keep Asami Sato from making the correct choice."

I furrow my brow, nodding slowly. "Asami's smart, though. She's not going to fall for a trick. I trust her."

"I do as well," the spirit says. "She is an ideal champion for this battle. But her victory is not yet assured."

In front of me, I see a tower of green light begin to grow. It branches out in many directions, and then many of these branches split as well. From the base of the green trunk, a red beam of light crawls upward.

"The path of time is like a tree. Early on, many possible futures lie open to us. But then we make choices," the spirit says. The red beam of light turns off, crawling up one of the branches. As it crawls up this branch, other branches fall away. "With each choice, we limit the possible futures that may come about." The branch the red light had climbed up shifts, becoming a new trunk. The green light climbs up again, once more branching off into various paths.

"The Eternal planned wisely. It is never possible to ensure a specific future will come about, but it was nevertheless able to set events in motion such that almost every outcome involved its victory." As Time spoke, the tips of most of the branches turned from green to a dark blue, leaving just a few scattered green branches. "Many humans would have made a mistake at one point or another, but ever since she has become aware of the Eternal's plan, Asami Sato has avoided any such mistakes. She did not always know what the best path was, but she was willing to ask for help when needed, and I was able to provide it for her. She chose wisely, always heading down the path with the greatest chance of a positive outcome."

The red light rose through the tree once more, making its way through the branches, heading toward one of the few green tips. At last, it came to a stop at a junction, one path leading to a blue tip, and the other to a green tip.

"At present, there are only two remaining possible futures, speaking in broad strokes. One in which the Eternal wins, and one in which it fails. One in which Izin Oum will become the one who shares my name, as the new destroyer of worlds, and one in which he will turn the power of death toward the cause of life, harnessing a force of destruction and using it to power humankind's path into the future."

My eyes widen as I hear this. "Those visions I had... They're the two possible futures, right?"

"That is correct," the spirit says. The tree it had used to illustrate its speech fell away. In its place, light rays traced an outline of Asami's figure, and then a sketch of my body lying prone in front of her. Above the image of my body, the rays traced an outline of Vaatu rising from it. "The events set in motion have guaranteed that one of those two futures, or something very similar, will come to pass. Asami Sato's actions will decide which of these futures it will be. She will of course endeavor for the brighter future, but she may not know the path to it."

I gaze at the image in front of me for a long minute. I don't know the path to it either, but Time couldn't be showing me all this for no reason. And I'm not out of the game yet, either, I realize. The corner of my mouth curls up. "Alright. I think I know what you want me to do."

Asami's eyes widened. Her gaze met with Izin's, but she was unable to read his expression for once. As emotive as his eyes normally were, for once they were unreadable. Maybe that wasn't surprising. With such a proposal, it was hard to say how he might react. He probably didn't even know himself how to react right now.

On the other hand, Asami knew exactly how to react. "No," she said. "This isn't the solution." Her eyes snapped back to the other spirit in the tree hollow, who the Eternal was currently using as its voice. "If you thought you'd be able to convince me that this was the right course, you would have done so in the first place. You wouldn't be holding your arguments back until you had no other way to stop me. So I don't believe you when you say that this is a good idea."

The spirit was silent for just a moment. "I knew I would not be able to convince you," it said at last, "but this does not mean that I am not right. It means you are allowing your irrationality to cloud your judgment, and you would have done so if I had explained in the first place. There is no reason to fear the darkness. It can be harnessed to a noble goal."

"If your goal is so noble, then why do you continue to hide it?" Asami said. "You still haven't told me what your endgame is. Making a new Dark Avatar can't be your final goal. What do you hope Izin will do?"

Once more, the spirit was silent. "It is not what I hope he will do," it said. "It is what I know will happen. As the new Dark Avatar, Izin Oum will restore the balance that the world has lost. Ever since the genocide of the Air Nomads, the world has drifted further and further from balance. This will soon be corrected."

Asami narrowed her eyes. The Eternal still wasn't telling her exactly what it had planned, but she was liking the prospects less and less.

"So…" Izin said. Asami turned to him as he spoke, though his gaze was now focused on the spirit. "Is this why I was born a nonbender? Because this was my fate all along?" His voice was steady, giving nothing away. Could he seriously be considering what the Eternal was offering?

"This is correct," the spirit said. "From the moment of your birth, you were shaped for greatness. Believed to be the eighth child of an eighth child of the Oum lineage, but without the expected bending ability of one in your position, the pressure placed upon you forged you into the man you have now become. A man who unlocked one of the most powerful secrets of reality, and who can guide the world as humanity decides what to do with it."

"A secret, what do you-" Asami began to say, but she found herself cut off. Ty Zen pushed herself forward, guiding Asami's lips to speak a different question. "Wait, what do you mean 'believed to be the eighth child of an eighth child'? I thought he actually was that?"

Izin turned to face Asami as she spoke these words, a faint hint of surprise on his face now. The spirit turned to Asami as well, and it shook its head. "The Lord Oum's mate prior to his wife bore him a child he never knew of. Izin was his ninth child, not his eighth. But this is irrelevant, as Izin was fated for another path, regardless of how many children his father had before him."

Asami was silent for a moment, making sure Ty Zen wasn't going to interrupt her again. It was a bit disconcerting that Ty Zen was able to do that, but at least Asami seemed to have full control of her body now. "Right. You said something about a secret of reality. What could possibly be so important?"

A moment passed, and then it wasn't the spirit who replied, but Izin. "The equivalence principle, you mean?" he said, facing the spirit now. "I know it's a big idea, but…"

"A big idea which will have profound consequences once humanity develops a method to harness it," the spirit said. It unsteadily took a step closer to Izin, its eyes opening just a bit wider as it looked at him. "You've done the calculations already, haven't you? The implications are obvious. If not you, then someone else will find a way to harness it. You must be in control. It's the only way to ensure this power is controlled."

"Wait," Asami said, stepping forward, between the spirit and Izin. She looked over at the spirit first. "Okay, let's start with this: What in the world does this have with making Izin a new Dark Avatar?"

The spirit's head tilted back as it looked up at Asami. "If I hadn't acted, Vaatu would have been reborn eventually inside the Avatar. By acting first, I can select the individual best equipped to resist Vaatu's influence. Izin Oum has had a lifetime of experience facing hardship and refocusing dark impulses toward positive goals. He can resist Vaatu's influence and be the dominant force of the Dark Avatar, using Vaatu instead of being used."

Asami narrowed her eyes. Izin did have a history of resisting dark temptations. He could have fallen in with the Equalists, but instead he'd sabotaged them from within. He could have turned against the Avatar, but he'd overcome his hate and built a successful life of his own. But Vaatu was something else. "No," she said. "As I said before, if you thought I would agree to this, you would have told me before. It's too late to get me to believe you now."

"Believe me or not," the spirit said. "It does not matter. Your only other choice is to allow Vaatu to be born free from my control. I assure you, this is the worst possible outcome."

Asami shook her head. "I'm not done trying to find another way," she said. She turned to Izin, meeting his gaze. For a moment, she didn't speak. She simply gazed at him, trying to form a connection. "Izin…" she said. There was hesitance in his expression right now.

Izin broke from Asami's gaze, shaking his head. "This might be the least bad outcome," he said. He turned his head to the side, closing his eyes. "All my life… maybe it's been preparing me for this. Maybe this is what I've been waiting for… my destiny."

"Izin," Asami said sharply. His head snapped back, looking over at her. Words came to her now, though she wasn't entirely sure if they were her own. "'Every time I've felt the world guiding me to something, it just ends up hurting me. Just because something seems fated, that doesn't make it good.' You told me that."

Izin blinked in confusion. "I did?" he blinked again, then shook his head. "No, I told that to my sis…" Izin met Asami's gaze again. "I told that to my sister, just before I passed out. How do you know that?"

Asami cracked a half-smile. She extended her hand, palm upward, and lit a flame above it. She extended her finger and twirled the flame around it as she spoke. "It's me, Izin. Do you really think this woman could have defeated the Avatar on her own?"

Izin's eyes widened. He gazed at Asami for a minute, before finally replying, "Well, I wouldn't entirely rule it out…" He chuckled and shook his head. "But I did say that, didn't I?" He slowly looked back over at the spirit. "But the fact that it seems fated doesn't mean it has to be bad either, does it?"

"No," Asami said. And it was Asami this time; she was sure of that. "We have to figure that out for ourselves. Tell me, Izin: Why do you think this might be a good idea?"

For a moment, Izin kept his gaze focused on the spirit. "...Because it's right. The world knows about equivalence now. It's only a matter of time before someone tries to weaponize it. I don't know how I can stop it… but maybe if I could put Vaatu to work for me, I could figure out how."

A flicker of blue in the corner of Asami's vision caught her eye. She looked toward its source even as she began to speak. "Okay, what exactly is the equivalence principle…?" she said. As she looked over in the direction of the light, she caught sight of Korra's body, which had now begun to glow blue. She might have to deal with that soon. "Maybe we can work together to handle it."

Asami's eyes were focused on Korra's glowing body, but she saw Izin slowly nod at this. "Maybe…" he said, then let out a sigh. "It's the equivalence between matter and energy. I was trying to figure out how to solve the speed of light paradox, and I couldn't get around it. Even at rest, matter is equivalent to energy. An enormous amount. So much, that if someone could figure out how to convert it…"

The world flashed blue before Izin could finish his sentence.

Equivalence: Death, Destroyer of Worlds

"It worked."

The voice comes first. Then comes the noise. The ground rumbles, the sky howls. They cry out in pain. They're being torn apart, faced with overwhelming energy.

Light comes next. The sky is on fire, lit with a brightness thousands of times that of the sun. The light illuminates the men and women alongside me, the shadows on their faces appearing almost pitch-black in comparison to it.

One of the men breaths slowly, gazing out the window with awe, bordering on fear. The woman next to him is stoic, almost emotionless, though her eyes betray a sense of wonder and her lips form a tight line. On the other side of her, a man turns his head down, closing his eyes.

I did this. An outburst of energy dwarfing even the explosion in Republic City, which had torn open a new spirit portal. All because of me, because of the equivalence principle, proven now in its ferocious glory.

One of my fingernails could have done it. Just a few grams, converted directly into energy, and this was the result.

It's far too late to remove the knowledge of equivalence from the world. If we hadn't done this, someone else would have. But we had. And now I would teach the world to fear it.

The world blinks. Reality unwinds.

Equivalence: Lightning in a Bottle

"It worked!"

The voice comes first. Then comes the noise. The ground rumbles, the sky howls. They cry out in wonder, experiencing the event alongside us. Energy cascades through them, though its source is thankfully distant enough from us that, overwhelming as it is, what we hear is only a faint whisper compared to its true might.

Light comes next. The sky is alive, lit with a brightness thousands of times that of the sun. The light illuminates the men and women alongside me, giving each of their faces an unearthly glow.

One of the men breaths slowly, gazing out the window with awe, with perhaps a touch of uncertainty. The woman next to him is stoic, almost emotionless, though her eyes betray a sense of wonder, and her lips slowly curl up into a smile. On the other side of her, a man leans his head back, closing his eyes.

I did this. An outburst of energy dwarfing even the explosion in Republic City, which had torn open a new spirit portal. All because of me, because of the equivalence principle, proven now in its wondrous glory.

One of my fingernails could have done it. Just a few grams, converted directly into energy, and this was the result.

It's far too late to remove knowledge of equivalence from the world. If we hadn't done this, eventually someone else would have, perhaps to use it as a weapon. But we had no such designs.

This was the easy part. The hard part was harnessing it. It will take many more years of work, but it will be worth it. There's enough fissionable material in the world to power all of humanity's endeavors for millennia to come. Not a permanent solution, but more than long enough for someone else to come up with something better.

The world blinks. Reality unwinds.

"What was that?" Izin said, panic in his voice.

The blue light… Korra's body wasn't glowing any longer. But now that it wasn't glowing, it was apparent just how close Vaatu was to being reborn. Tendrils of darkness were slowly beginning to grow from her stomach, reaching outward. "It was Korra," Asami said. The imminent threat had gotten her mind to run in overdrive, piecing the clues together about what had just happened. She turned back to Izin. "Back during Harmonic Convergence, she connected with the cosmic energy in the Tree of Time, assuming a spirit form. She must have connected here as well to show that vision… those visions to us.

"That's what you're afraid of, isn't it?" she said, connecting her gaze with Izin's. "What someone might do with knowledge of the equivalence principle?"

Izin nodded slowly. His body seemed to shake slightly as he spoke. "Exactly. That was…" Izin shook his head. "It can't happen that way."

"It doesn't have to," Asami said. She reached forward, placing a hand on Izin's shoulder. She waited until he looked up, meeting her gaze. "Not the first way. Remember, there were two visions. In the second vision, it was only a test, not the final goal. Maybe even the most destructive forces in the world can have some uses for good. Even Kuvira's spirit weapon had the benefit of opening up a new spirit portal, after all."

"This," said the spirit off to Asami's side, "is what I have been trying to convince you of. Even Vaatu can be used for good."

Izin glanced over at the spirit, but Asami quickly placed her other hand on his other shoulder, prompting him to look back at her. "Don't listen to it. That was a vision of your future. What you might become with and without Vaatu. Do you really think the version of you who merged with Vaatu is going to be the one who doesn't want to weaponize that power?"

It only took a moment after she said this before Izin let out a chuckle. "Of course not," he said, a smile on his face now. "You're right. Vaatu isn't the way. He can't be."

Asami allowed a smile to cross her face. She'd done it. She'd gotten through to him.

"It is unfortunate that you feel this way," said the spirit, grabbing Asami's attention once more. Asami let go of Izin's shoulders, turning to look at the spirit now. "This will make matters significantly more difficult for me. But not, however, impossible." The spirit slowly raised up one of its hands.

The light in the tree hollow seemed to dim. A sinking weight in her chest, Asami turned around, toward Korra's body, gazing upon a sight which chilled her to the core. Tendrils of darkness reached out to either side of Korra's body like arms, pushing against the floor. Slowly, a thin, dark body pulled itself out of Korra's stomach. Vaatu, just as Korra had described him.

"No…" Asami said. In the back of her mind, she could feel Tenzin and Katara's spirits becoming gripped with fear. Ty Zen seemed to be filled at rage, most likely at the prospect of Izin becoming possessed by Vaatu against his will. Kuvira… was oddly calm.

It's not too late, Kuvira said within Asami's mind. Don't give in just yet. You still have options.

Asami breathed slowly. Right, she replied. She still had bending abilities, after all. If she had to, she'd try to defeat Vaatu herself before he could possess Izin. If she won, they'd just be back to where they started. "Izin…" she said. "Run."

Izin glanced at Asami for just a minute. Their eyes met, and he nodded. He made a dash for the exit from the tree hollow, but one of Vaatu's tendrils snapped forward and wrapped itself around him before he made more than a couple steps. It was so fast, Asami wasn't ready to react before it had happened.

"Did you really think it would be that easy?" Vaatu said, his body moving in closer to Izin. "It is over. Simply accept your fate and this will all be much easier for all of us."

Izin slowly shook his head. "I… can't. I can't let you do… that…"

"You fool!" Vaatu said. His tendril squeezed Izin tighter, pulling him closer. "You and your kin have let yourselves become a cancer on humanity. You push recklessly toward the future, not knowing what it might bring, leaving the destruction of your entire race as the only possible outcome. I am trying to save you from that. Humanity must be shown to fear this power. They must be cowed into giving up their dangerous quest for ever more knowledge and power over nature. It is the only way to restore balance."

"You're wrong," Asami said, stepping toward Vaatu. So this was the Eternal's true goal. It wanted to turn Izin into a Dark Avatar so that he would make humanity fear him. And by extension, they would fear progress. "We don't have to be afraid of progress. Change is inevitable, and fighting that is what will lead to suffering. We've seen a future where this power is to be put to a good use."

Vaatu turned, facing Asami now. His body seemed to glow with darkness as he spoke. "A future filled with fools who think they can contain such a power. Do you seriously believe they can so?"

"I do," Asami said. She took a step toward Vaatu. Her heart was pounding in her chest right now, but she wasn't going to let fear overcome her. "The better side of humanity will win out. It always has."

"Believe it if you wish. That doesn't make it true," Vaatu said. It turned to Izin once more. "It is time we finished this."

"No," Asami said. She could feel Ty Zen's rage burning within her right now, and it was just what she needed. She squeezed her hands into fists, and fire burst out to encompass them. She punched forward, shooting a ball of flame at the tendril which had encompassed Izin. The tendril recoiled from the blast, but two more quickly shot out from Vaatu's body to hold onto Izin. Another tendril shot out toward Asami, but this time she was ready for its speed, and she managed to dodge it.

"Darkness cannot be defeated," Vaatu said as he continued to attack Asami. Asami was able to ward off its attacks with a rapid barrage of fireballs, but it quickly became apparent that this was a losing battle. She needed the power of the Avatar to fight against Vaatu, and that wasn't an option now. "You know this. Accept it."

Asami shook her head. As Kuvira had reminded her, she still had options. "I might not be able to destroy it," she said, jumping out of the way of one of Vaatu's tendrils. "But I can defeat it." She let Ty Zen's rage fuel her strength, and she extended her hand outward, heating the fire around it. "I don't need to destroy Vaatu to win," she said. "I need to defeat the Eternal. And it's just given the game away."

Vaatu let out a laugh at this. "Have I?" he said. "You truly are more foolish than I thought. To think I was so worried that you might foil my plans that I ensured Sheng couldn't restore your voice! Apparently I needn't have bothered." Vaatu shot out a cluster of tendrils at Asami, but she brought up her free hand to generate a wall of fire in their path.

"You can believe that," she said, glaring at Vaatu and spitting his words back at him. "That won't make it true. You've told me how to defeat you. You fear progress. You fear the future. So that's what I'm going to give to you." Asami extended her hand, pointing it at the wall. As her wall of fire temporarily kept Vaatu's attacks at bay, she continued. "Varina explained the role of this tree to me. It grows in concert with the Tree of Time. This tree holds onto the past, keeping the world from progressing too quickly. So what do you think will happen to the world if I burn a hole in it right now?"

For just a moment, Vaatu's attacks against Asami's firewall stopped. "You wouldn't. You have no idea what chaos it will bring."

"I know it can't be worse than what you're planning," Asami said, narrowing her eyes. A grin slowly spread across her face. She had it. "And I know you'll hate this a ton more than I will."

A moment passed, and then Vaatu let out a laugh. "A valiant effort," he said. "Perhaps I didn't underestimate you after all. There is just one problem with your plan: This tree has weathered more than you can possibly imagine. Your simple firebending cannot hope to damage it."

"Are you sure?" Asami said. She squeezed her fist, and the fire surrounding it turned blue, and then a bright white. "When I needed a firebender's help, I asked a helpful spirit to guide me to the most powerful firebender I could get to assist me. I got Ty Zen Oum, Izin's sister. And if I'm not mistaken, she was born immediately before him, right?"

Right, Ty Zen said. Asami could tell from the tone of her voice that Ty Zen had come to the same realization as Asami had.

Asami nodded. "You told me yourself that the Lord Oum had a child he never knew about, which led him to mistakenly think Izin was his eighth child. The eighth child of an eighth child, fated for something great. But Izin wasn't the eighth. Ty Zen was." Asami could feel the heat radiating off her hand. Ty Zen was mostly keeping it contained to the fire, but with how hot the flame had gotten, even her efforts weren't quite enough.

"She… her power is irrelevant. She was never trained to use it," Vaatu said, though Asami could hear uncertainty in his voice. "I averted the course of fate so that her power would never come into play."

"Well you were wrong," Asami said. The flame surrounding her hand seemed to be boiling now, and sparks danced within it. "If anyone can burn a hole in this tree, she can. So you have a choice: Give up, or we see what happens when I release this flame."

For a long minute, Vaatu was silent. Asami forced herself to keep her face steady. She couldn't let her own fears show through right now.

Finally, Vaatu spoke. "We cannot release Vaatu. This would be the worst outcome for all of us."

Asami grinned, letting her body fill with relief. "He spent ten thousand years imprisoned by the Avatar in the Tree of Time. He can spend the next ten thousand here. I figure being his jailor is a fitting punishment, after what you've tried to do."

Through the wall of fire, Asami could make out Vaatu's tendrils retracting from around Izin. "Agreed," he said simply.

Asami let out a sigh, closing her eyes for a moment. It was over.

Author's Note: This chapter pushes the wordcount for this fic over 100,000 words, making it easily novel-length. Thank you everyone for sticking with me through this. I have plans for an epilogue to tie up some final loose ends, so stay tuned for that.

Oh, and don't say I didn't drop hints about Izin. I may make a list at some point, for those who missed them.

As ever, any and all comments and reviews are appreciated!