O'Shovah: Renegade, Chaos, or Necron?

So... Who's got ideas on why exactly Farsight left the Tau Empire?

I think the Dawn Blade is a Necron artifact, just because of its description- it has an unknown energy reading and cuts through flesh / armor like Warscythes. The structures on the planet where he found it were xeno (according to an Inquisitorial report), but they don't specify what species. Could have been ancient Tau buildings, Necron (the planet was a "Dead World", could've been a Necron Tomb World), or some other unknown species... but the Tau are like the Necrons in that they avoid the Warp for everything. They have no psykers, they don't use it for travel, et cetera. Then again, there's the fact that T'au was saved from the Emperor's Great Crusade by a Warp storm. Could have been accidental, or the Chaos Gods (or just one) could have plans for the Tau, so it could also be Chaos who is controlling (or influencing) O'Shovah.

this is one of the times that i wish i knew fluff

This topic has been debated ever since his info came out.

As for what I believe...

I believe his experiences in war embittered his outlook on life. Having been under siege for a whole year without any support and watching his troops fall, he began to have doubts about whether the Greater Good was really his good. The death of his Ethereals was what gave him the impetus to follow his true beliefs and the Dawn Blade was a neat little trinket that he picked up on his way.

The Dawn Blade has some power to null heavy armor. It also crackles with unknown energies. So where does it come from? I don't believe it's of necron origin, because it would be made of living metal, which it obviously isn't. I don't think it's of chaos origin, since Chaos and Tau are like oil and water. They don't mix very well. It's more likely that if it was of chaos origin, it is just a piece in Tzeentch's grand plan for the universe.

It could even be Anaris, the greatest Sword of Vaul, which fell to the mortal realm after the dissolution of Khaine. Who knows, really?

Back to Farsight.

I believe he still follows what his "Greater Good" is and is still a non-traditional ally of the Tau if they need him, but he would prefer not to come back into the fold because he believes the ideals and beliefs in the Tau Empire are stunted and overhierarchical. We'll see what happens.

I looked it up, and I do think it's a Necron weapon, but it doesn't have hold over him. It can't be Chaos in origin, cause like you said Chaos and Tau don't play nice together. I don't think that the original Farsight is still alive though. There's no way a weapon could extend his life, no matter where it came from. The reason (or what I think) why he defected, is because he's sick of bureaucrats trying to rule over trained, and dedicated warriors. He represents the struggle between state, and military. Whether warriors should rule, or bureaucrats. He's sick of tau who have never seen war commanding where they should march, and die. That's what I think anyways.