[The roar came out of you before you decided to make it.]
[It filled the ash-choked air around the palace walls and rolled outward into the grey sky, the sound of a body that had just finished transforming into something it had not been before and was announcing the fact to whatever could hear it.]
[The bone armor had closed over your skull completely. The plates were continuous now, thick and dense, the azure color settled into a deep, consistent tone. The only things remaining above the collar were the high topknot, moving in the heated air your body was generating, and your eyes, which had gone fully red and were providing their own light.]
[You felt the power running through you.]
[It was not psychic. It carried none of the particular quality of Warp-touched ability. What moved through your body now was purely biological in origin, the product of genetic engineering taken to a place that no standard human or Astartes or Primarch gene-craft had ever gone. The ancient race whose remnant technology had rebuilt this body from the inside out had understood something about the potential of organic systems that the Imperium's own scientists had never reached. The power was deep and structural and felt like it had no ceiling you had yet located.]
[Your feet came down on the solid ground and the ground stated its objection in the form of radiating cracks that spread outward from each impact point. You had surpassed five meters. The bone-shell added mass and height both, and the result was a frame that made Fulgrim, who had not entered and had apparently decided not to enter his ascended Daemon Prince form, look like the smaller party in this confrontation.]
[Fulgrim was smiling.]
["Brother. You keep producing things I did not predict. I find this very satisfying."]
[The narrow sword was gone. In its place, two curved blades had materialized in his palms, each one wreathed in the particular purple light that Slaanesh's attention produced in weapons it had touched. He shifted his stance, read the geometry of your armored chest, and attacked.]
[The blades found the chest plating and drove in.]
[At the same moment, four azure bony limbs erupted from the broad surface of your spine, extending outward from deep within the musculature with a speed that matched the curved blades. They drove toward Fulgrim from four angles simultaneously, and three of them connected, punching through his ornate power armor and into the body beneath.]
[Neither of you stopped.]
[Fulgrim pressed both curved blades deeper into your chest with the deliberate intention of widening the wound into something that could not close easily, his face settling into the focused expression of someone pursuing a very specific aesthetic objective. Your expression did not change. Your arms came up, the bone-plated fingers extending into tentacle configurations, wrapping around Fulgrim's arms at the bicep and locking them in place.]
[You dropped your head and drove it forward into his face.]
[The impact was not technical. It was total. The bone-armored skull connected with Fulgrim's features at full Primarch-scale force, and the face that had been the most beautiful in the Imperium and had only grown more elaborate under Slaanesh's cultivation collapsed inward across the nose and cheekbones with a sound that echoed off the palace wall behind you.]
[Fulgrim coughed purple blood and made a sound that, coming from anyone else, would have been distress. Coming from him, in his current relationship with sensation, it sounded like gratitude.]
[His magnetic boot came up and hit your chest and abdomen with enough force to snap the tentacle holds.]
[Both of you separated.]
[You were moving backward through the air and you assessed the situation in the available time. The four bony limbs that had been anchored in Fulgrim's body withdrew as you flew, repositioning as you fell, and before you reached the ground they had driven themselves into the earth and arrested your momentum. You hung for a moment, suspended at the ends of four azure struts, then found your feet and pulled yourself upright.]
[The damage across your body was already closing. The bone plates were rebuilding across the cracks and impact points, the flesh beneath cycling through repair at a rate that had stopped requiring your attention. Across the open ground, Fulgrim was doing the same, the purple light moving through his wounds with its own reconstructive purpose.]
[You exhaled a breath that came out too hot for the temperature around you.]
[Your neck cracked as you rolled it, a sound like settling stone.]
[Your eyes had not left him.]
[The four bony limbs retracted fully into your spine. Your arms moved, the configurations building: the left arm resolving into a scythe-limb curved like a crescent blade, the right thickening and hardening into the proportions of a war hammer, the bone dense enough to register as a distinct material from flesh. The weapons assembled themselves from your own biology without requiring conscious construction.]
["Come again, traitor."]
[The words came out with more feeling than you had intended to put into them. You moved toward him.]
[Fulgrim came forward at the same moment, the curved blades rising, and the two of you were three steps from contact when the passage beneath the wall behind Fulgrim's position opened and the figure came through it at a full run.]
[Golden power armor. Adamantium storm shield carried at a combat angle. A chainsword in the other hand, its teeth cycling, a weapon that had been built for a Primarch's grip and was currently being used at full extension. White hair. The forward momentum of a man who had seen the fight from the passage entrance and had calculated his entry angle on the move.]
["Fulgrim!"]
[Rogal Dorn hit Fulgrim's flank at speed, the storm shield driving into his side, and the chainsword Stormfang came down across the back of Fulgrim's spine in the same motion.]
[You brought the scythe arm down across Fulgrim's head and drove the bone-hammer deep into his shoulder blade in the same instant.]
[The impact on Fulgrim from three simultaneous strikes went outward in a spray: purple blood, shattered armor, fragments of the ornate plate that had been crafted to be the most beautiful in all the Legions, scattered across the ground and across the armored surfaces of the two Primarchs now standing over him.]
["Yes!"]
[Fulgrim's voice, coming from beneath the pile of damage that had just been applied to him, sounded genuinely delighted.]
[His body began to move differently. Something was emerging from his lower back, the proportions shifting, the scale beginning to climb toward what came next. A serpentine form, the first suggestion of the Daemon Prince configuration that Slaanesh had been holding in reserve for exactly this kind of moment.]
[It stopped.]
[The Emperor's spiritual presence enveloped the Palace of Terra like a blanket drawn over every surface, present in the stone and the air and the light, and where it touched Fulgrim's expanding form, the expansion ceased and then reversed. The half-manifested Daemon Prince configuration was pushed back and back until there was nothing left to push, and Fulgrim was gone, returned to wherever the Warp sent its investments when the material world rejected them.]
[The ground where he had been was marked with purple blood and the ash continued to fall and the sound of the siege continued above the walls.]
[Boom. Boom. Boom.]