I know I promised Eldar or Tau, but I got a good idea for Chaos and just rolled with it. Anyway, enjoy.
Abbadon was pleased. He had done it. With the Orks on the rampage after Armageddon had fallen, more and more of the Imperial Guard had been sent away to deal with the Xeno threat. Sensing a weakness, he had pounced, launching his umpteenth Black Crusade (count had been lost, Abaddon himself insisted it still was the thirteenth and the lulls in between were merely breaks), and this time he had succeeded in taking that blasted Cadian Gate. The only slight dampener on his spirits was currently cowering in front of him on the floor of the balcony he was currently standing on, having temporarily interrupted his victory celebration.
"Milord, I am afraid bear bad news." the cultist said.
"What is it?" said Abbadon annoyed. There was a Slaaneshi deamonette due to preform a stage act soon, this message would better be important.
"It concerns the Planet Killer, milord. I'm… The fleet master fears it has… um… gone missing."
Abbadon's outcry of rage could be heard on the other side of the planet.
"WHAT?" Abbandon shouted, foaming at the mouth. Sure, an unusual number of ships had disappeared recently, from both Chaos and Imperial fleets, but his own personal flagship? That kind of incompetence got people killed. Messily and slowly.
"Tell me, how exactly did this happen?" said Abbadon in a sweet voice, that was somehow more terrifying than the usual thunderous yelling.
"Um, nobody knows exactly milord." said the cultist, thoroughly soiling his pants by now. The moonlight glistened of his brow as sweatdrops rolled down his forehead.
Strange, Abbadon didn't remember Cadia having a moon. Looking up, he saw a huge shape slowly making it's way across the sky towards the Chaos fleet.
"That's no moon…" he whispered in shock as realization dawned. Meanwhile, the cultist got a message on his vox.
"S-Sir? The fleet master just called. He has found the Planet Killer again. As well as those other dozen missing ships."
Gazghkull looked to the main view screen from his shiny new command throne. At first the thing had protested against his presence, but after sitting down really hard a couple of times it had shut up. On the view screen was Cadia, with a bullseye drawn over its center.
"Boss to Dakka Control, ya gits ready?" he said through the internal coms.
"Sure fing boss. Push da button ter fire." came the reply. Gazghkull stood up, and clanged a couple of times with his powerfist to get the boys on the bridge to pay attention.
"Alroight ya gits-" he said, posing dramatically, "I'M FIRIN' MA DEFF GUN!"
He rammed the firing button.