So far I considered a love story between my char Synthoras, which used to be a black heart Warrior, and a hekatari from the Red grief. During a raid to a necron tomb-world Vect secretly gave the order to thin ranks, due to a little insurgence of a trueborn group demanding for more loot. Synthoras was between those who were betrayed and shooted once reached the inner sanctum of a Lich lord tomb; his love with her sisters were shooted too cos witnessed the event and she charged the trueborn for saving Synthoras. On the brink of death his last image was her face looking at him, lifeless, with just a bloody tear running down her cheek.
In the total darkness and cold of death a voice whispered to Synthoras, asking what he truly desired; ofc he replied "vengeance".
Long story short hidden in the sanctum there was a very tiny shard of the nightbringer who gave strenght to my char with the promise to help it regain freedom, who put it in a soul trap taken from a drakon's body there and escaped the tomb. Now if you have ever seen pitch Black/Riddick you can figure him getting back to his old pals, enjoying a sadistic, devious and ruthless bloodshed, taking one by one the traitors, stealing a ship for getting back home seeking vengeance and, driven by the shard, collecting more parts of it since pacts with badasses like c'tan must be fullfilled. That's the main plot to kick some necron asses...I just need to justify the other factions
"Cruel fantasies of someone's dreams...that's what we are; They call us forgotten tears 'cause no eyes cried for our griefs"
Synthoras, Archon of the Forgotten Tears