To see which Earth is worthy of surviving? That's the only reason I can think of. And we don't know who set it up, or if it's just some natural phenomenon to our universe.

But... regardless of how it started, you can't break the contract. Most of the others signed without knowing what would happen. I stepped up later, to fill one of our empty pilot slots. I knew what would happen.

[He knew he was going to his death. But what else could he have done?]

I had to protect the world that my adopted sister died for. She was younger than us - only ten.