The Legend of Korra, Season 2

Wan:
[to Raava and Vaatu] Stop, or you'll destroy everything!

Raava:
This doesn't concern you, human!

Wan:
It does when the lives of spirits and animals are in danger!

Vaatu:
If you are a friend to the spirits, then use your fire to help me break free!

Raava:
Don't involve the human! This is between us!

Vaatu:
[frantically] Please! Save me! She has tormented me for ten thousand years!

Wan:
Ten thousand years? [attacking Raava] Let him go!

[Wan weakens Raava's grip on Vaatu. Raava swats the young man away. Vaatu pulls further from Raava, until only one tendril holds the two spirits together. Wan, recovering, sees this and uses his firebending to separate the two spirits. Vaatu flies away from Raava, and stands atop a nearby mountain to address Wan.]

Vaatu:
Thank you, human. You have preformed a great service for the spirits. [Vaatu flies away]

Raava:
[to Wan] Do you realize what you've done?!

Wan:
Yeah. I helped a spirit who was being bullied by you!

Raava:
You are gravely mistaken. I was keeping him under control.

Wan:
And what gives you the right?

Raava:
You don't even know who I am, do you?

Wan:
Should I?

Raava:
Yes. My name is Raava. That spirit you freed is Vaatu. He is the force of darkness and chaos. I am the force of light and peace. Since the beginning of time, we have battled for the fate of this world, and for the past ten thousand years, I have kept darkness under control and the world in balance. Until you came along.

Wan:
So, by freeing Vaatu, I let chaos into the world?

Raava:
Precisely. The human and spirit realms are heading toward annihilation, and it's all your fault.

[cut back to Korra in the present day]

Korra:
[quietly] Raava, I found you.