Author's note: This fanfiction idea came to me after reading a meta written by kalz-one on Tumblr about how the Necromongers were able to betray Riddick.
This is set post Chronicles of Riddick and pre-to-start Rule the Dark, but draws on imageries from both movies.
A cage around his head
The silent applause of the whole armada was deafening, the clank of armored (and naked) knees onto hard floor rippling like a thunderous wave over Necropolis. The Lord Marshal was dead, the ornate knife once buried in the back of Irgun, a Necromonger soldier now buried deep in the skull of the Lord Marshal. It liked the taste of Necromonger blood.
You keep what you kill.
They gave him the Basilica ship within which Necropolis was housed; they gave him food and water and booze when he demanded them; they gave him the Lord Marshal's room and gave him a bed; they gave him their women, and he buried himself balls deep into them, enjoying their moans and cries but ignoring their soft pleas for him to go back to bed.
They gave him the run of the ship and the run of the universe.
They gave him his knives and other blades besides, calling him 'Lord Marshal', hammering out a new armor with more blades hidden deep within the harsh shadows of folded metal. The title was a noose draped around his neck, and when it was finally completed, the helm was a cage around his head that he let them put on.
But he took no vow – the vow that every Lord Marshal was required to take, from Covu, The Transcended, to Zhylaw, The Last, the vow of every Lord Marshal to take the Necromongers to the Underverse. He had no wish for tradition, and though he took their bread and salt, he was not one of them.
Fed well and possessing creature comforts, he never saw the bars of the cage closing in, the noose tightening. But even a caged creature could see through the bars, and he could still see and turn when the first few attempts on his life were made. Yet still he remained, an accomplice to his own downfall, when Vaako dangled the bait of Furya before him.
He fell, cage and all, the years of his needs being met barely a cushion for his fall. He climbed from the ruins of the rubble, dragging his body and one useless foot behind him on Not-Furya, leaving behind the shattered cages of civilized behaviour.
Time to find that animal side again.