Darkin question and Theory
Quick question for any Rioter reading this. Both Aatrox and Rhaast have a similar red and grey design, however Varus in his updated splash is more purple... Is this because Varus' splash was drawn to match his current in game model? Or are Aatrox and Rhaast actually blood brothers (hence similar design) and we should expect to see variations in the remaining Darkin?
Onto the theory, with the reveal of the new Aatrox, we got some snippets of what his new lore is going to be. Apparently the Darkin were once protectors of Shurima against the Void and had a previous alliance with Targon's Aspect of War.
: "Hail Pantheon! Let me hear you cry of friendship! Let me hear you scream of Brotherhood!" to
: "I know it was you trickster! You gave them the tools to trap me!" Come! Let me kill you... a thousand times isn't enough!" to 
Based on Aurelion Sol's lore we know that Ancient Targon, is a space farring empire, that have dominion over parts of the universe. I compare them to a 'Space Noxus' conquering and expanding territory. In Varus' lore we were given the impression that the Darkin were a world conquering race that roamed the galaxy. With Aatrox's quote of Pantheon's betrayal these 2 line up imo. The Darkin and Targon were partners of sorts in Targons protection of the universe against the Void, and they did so by expanding their territory. So when the Icathians opened the Void portal in Shurima, the Targonians dispatched the Darkin to assist the Empire of Shurima. But somewhere between their noble mission and the Darkin war, either the Darkin turned on those they sought to protect or they were truly betrayed by Targon. Resulting in Zoe providing the mortals with the spells needed to imprison the Darkin. Varus would then be recruited for the second wave in their invasion of Runeterra or possible as back up against the backstabbing Targon.
It makes sense that they were once 'protectors' its a plot twist in their backstory as a race and links them to Runeterra and other factions while simultaneously fleshing them out as extraterrestrial beings. It more of me piecing together what we know opposed to any grandiose extrapolation.