Editing Sky Serpents (section)

===Events on Prospero===
Maybe he lures Xun down into the reflecting caves on the pretext that he'll explain what is going on, since Anshul believes that once Xun knows about the true nature of Chaos, Xun will join him.

So Xun goes down to the reflecting caves, to meet Anshul and send his message.
The two forces meet under parley, like the Night Lords and the Dark Angels do in that one story. Across the surface and in orbit, the two legions stand facing each other. There's even some friendly chatter across lines, but mostly everyone waits.
Xun sends his message, which is part of the traitor plan anyway and then he has his talk with Anshul. Suffice it to say that it doesn't go well.
There's a grippy vision of a thousand different heresies, ones where the roles are reversed, ones where Anshul and Xun stand united against a mad Oramar, ones where Xun bears the sigil of the Wolf and Anshul has but one eye, ones where the Warmaster is named Hektor.
And then they start fighting, the planet itself becomes unstable.
The two legions tear into each other, the world quakes.
Both have to leave the planet and because of Anshul's trap, the price of Xun's escape is the curse on his legion. It's the taint of Prospero and they're forever intertwined with that world.
That's why Xun goes there, thousands of years later, to ascend.