Emperor's Children - Angel Exterminatus: As Horus' rebellion ground on, the Iron Warriors took the time to humble their great enemies, the Imperial Fists, upon the isolated world of Hydra Cordatus that the Sons of Dorn had recently brought into Imperial Compliance. Following their victory, word reached Perturabo that Fulgrim and his Emperor's Children Legion, wished to rendezvous with him to discuss something of great import.Though the Phoenecian had yet to reveal the true purpose of his visit, he had promised Perturabo that it was "wondrous." Perturabo knew that his brother had a flair for the melodramatic, which only seemed to have gotten worse since the IIIrd Legion threw their lot in with the Warmaster.The Lord of Iron counted none of his fellow Primarchs as close friends, but the Phoenician's adherence to perfection in all things had once provided common ground between the two superhuman warriors and allowed them to talk as trusted comrades-in-arms if not beloved brothers. What the Emperor's Children had sought with constant movement towards the attainment of perfection, the Iron Warriors earned with rigid discipline and methodical planning; two divergent paths to the same ultimate goal.Perturabo believed Fulgrim's visit had something to do with the inevitable campaign to be conducted against Mars. The Warmaster needed the Martian theatre fully secured before they moved against Terra, and he believed that Fulgrim was there to seek the Iron Warriors' aid in breaking open the forge-cities of the Mechanicum. If he was right, Perturabo wanted his Legion to have a plan in place to achieve that objective.Until the Iron Warriors received further orders, Perturabo would humour his brother and listen to what Fulgrim had to say. While making plans for the upcoming campaign, Perturabo received word that the Emperor's Children had arrived, unannounced, on the surface of Hydra Cordatus. Over three hundred drop-craft had landed beyond the mouth of the valley where the Iron Warriors had made their encampment.The IVth Legion quickly gathered in formation to honour the IIIrd Legion with a vanguard to receive them. Battalions of Thorakitai Imperial Army troops stood ranked in their tens of thousands. Before them stood two hundred Grand Battalions of Iron Warriors, fifty thousand warriors in amberdust-burnished warplate. Such a display of might and magnificence had not been seen since the slaughter unleashed upon the black sands of Istvaan V.Yet Perturabo and his senior officers looked on in awe at the gaudy cavalcade of noise, colour and spectacle that emerged from the IIIrd Legion's drop site into the valley. Fulgrim and his Emperor's Children were now completely unrecognisable from the honourable warriors that had once formed the IIIrd Legion. Perturabo knew something fundamental had changed within the Emperor's Children, but could not imagine what purpose the disfigurements and degradations its warriors now sported could possibly serve.Fulgrim met with his brother Primarch in the private inner sanctum of his command bunker with an enticing offer that Perturabo could not refuse; the means to make it so that the Lord of Iron's every desire could be made real and would never disappoint, never fail to live up to his fondest expectations, and never, ever be eclipsed. Fulgrim came with an offer to unite their mutual forces in battle on a glorious quest. One that might tip the balance of the Warmaster's rebellion.Though Perturabo was suspicious of his brother's intentions, perhaps this joint venture would grant understanding through common cause. Fulgrim revealed his purpose; they were to venture to the Warp Storm that had plagued Perturabo's dreams all of his life. Within it was hidden an ancient and forbidden xenos weapon known as the Angel Exterminatus. It had been hidden in the grave of its doom, a weapon of such power that the stars themselves turned upon it rather than allow it to escape its prison.