The only thing I borrowed from the Halo novel "Fall of Reach" is the time/date and location, plus the first whole page, and a a few sentences from the second page of Chapter Thirty-Three. Also I own neither any claim to Halo or Warhammer 40,000 except the idea of this story.
0534 Hours, August 30, 2552 (Military Calendar) / UNSC Pillar of Autumn, Epsilon Eridani System
The Pillar of Autumn detonated its port emergency thrusters. The ship slid out of the path of the asteroid, missing it by ten meters- The Covenant plasma trailing them did not. It impacted the city-sized rock and sent fountains of molten iron and nickel spewing into space. Nine of the ten teardrop-shaped Covenant fighters- nicknamed "Seraphs" by ONI-dodged the asteroid as well. The tenth ship slammed into the asteroid and vanished from the bridge's view screen.The other single ships accelerated and swarmed around the Pillar of Autumn, her with pulse laser fire.
"Cortana," Captain Keyes said, "activate our point defense system." The Pillar of Autumn's 50mm cannons flashed-chipping away at the Covenant ships' shields. "Already engaged, Captain," Cortana said calmaly. "Ensign Lovell," Captain Keyes said. "Engines all stop and bring us about one hundred eighty degrees. Lieutenant Hikowa, ready our MAC gun and arm Archer missile pods A1 through A7. I want a firing solution that has our Archer missiles hitting with the third MAC round." "On it, sir," Lieutenant Hikowa replied. "Aye, sir," Ensign Lovell said. "Answering engines all stop. Coming about. Brace yourselves." The Pillar of Autumn's engines sputtered and died. Navigational thrusters fired and rotated the ship to face the real threat-a Covenant carrier.
Suddenly a brilliant green light appeared out of no where blinding the entire bridge crew. "Cortana," Capitan Keyes said, "status report, on the double!" "Sir," Cortana replied " our radar is picking up multiple large metallic objects ahead and around us." "bring it up on the view screen." Keys said. "Done sir" Cortana replied. Looking at the main view screen, keys could see several large warships that dwarfed his cruiser in size. What amazed him though was the ship they were in formation around. It was easily four times the size of a Covenant carrier, bristling with large gun mounts from stem to stern, it was also covered in a Goth artist wet dream's worth of gargoyles and angels. But what was most shocking about it was the massive golden double headed eagle on the things prow. The head on the left was blind, while the head on the right had an eye.
Keyes was pondering what it's meaning was when Cortana said "Captain, look at the Covenant Carrier!" "Oh my God." Keyes said softly. What appeared to be on of the newcomers ships was fused right at the mid-section of the Covenant carrier. "Cortana, can you explain what exactly happened there with that Covenant carrier and that other… ship?" Captain Keys asked "Negative" Cortana replied "I was as blind as you all were due to that green light." "What do you mean?" Keyes said curiously " I mean that that when that light appeared I had to act as fast as I could before it overloaded every single one of our sensors." "wait were picking up multiple transmissions on several channels." Cortana said matter of factly "There is multiple Covenant inter-ship chatter, things about Demons onboard and multiple hull fractures" "What about the other frequency?" Keys asked? "I don't know I can't quite understand it, it sounds like multiple Earth languages but I can't be sure. Give me some more time to try and translate it." "Very well" Keyes responded. "But do hurry it appears they aren't expecting guests." At that remark several of the new ships had veered out of formation on the Huge capital ship and turned towards his ship. "Definitely not expecting guest." Keys muttered. "What do we do sir?" Hikowa said. "Let's not be hasty, after all they out gun us like…" "seven to one" Cortana interjected. "Exactly so lets see what they what, Hell they might even be here to help."