During the battle of Reach.
Someone wearing an ODST armour is running down a hall way in a secret underground ONI facility, his mission is to destroy the facility and all it's secrets.
The battle was lost, no the battle was lost the moment they found Reach.
Now it's only a matter of time till the enemy overwhelm the last of Reach's orbital defences and destroys of what remains of the navy.
While the brave navy men tries to fight the enemy with its battered fleet from the last engagement while hopelessly out gunned, out numbered and without any hope of reinforcements.
While the heroic marines and armies of the UNSC makes it's final but futile last stand against enemy landing parties before being overwhelmed or helplessly glassed from orbit.
While they die a glorius but meaningless death (for the most part) It is up to the him to do the job that is the most important while will never be mention in the history books, that is if humanity survives, while the others fight a meaningless lost battle and be remembered his and others like him will do the most important job and die in the shadows and be forgotten by everyone else.
Such is the fate of being an ex-spartan candidate, even if you didn't make the cut ONI still has many other uses for you.
In his his case being ONI's private hitman squad disguise as ODST.
His mission is to destroy and prevent valuable UNSC assets from falling in to the enemies hands.
The rest of his squad died in an ambush by cloaked elites.
Now their energy swords are strapped on to his thigh as souvenir also incase he runs out of amunition and has to fight in melee.
As he was running down the hall way to his target the floor suddenly a loud bang could be heard.
"crap! They finaly breached the door" he thought before renewing his efforts with hast.
He finally reached the end of the hall way, now facing a set of metal door.
The door required a pass code to be opened.
He immediately typed in the code and the door slowly slid opens.
He didn't wait for the door to fully open before stepping in and closing the door.
Once the door closes he slashed the controls preventing anyone from going in and out.
He turned around and saw a modified UNSC halberd destroyer armed with new experimental weapons and shielding, it's one of ONI's pet project.
A prototype for Infinity so to speack, the project's aim is to try out new technology on a smaller scale before moving on to something big like infinity.
Seeing a ship a thought flashes through his head but he quickly dismissed it "well it's useless to think about it now, the hangar door on the surface was melted by covenant glassing beam and the ship doesn't even have an AI."
Even if he manages to to pilot a ship that is suposed to be crewed by a hundreds and get pass the meter thick hanger bay door theirs still the entire covenant fleet to fight.
He quickly enters the ship and made his way to the control room.
In the control room, he started up the ship and immedeatly tries to overload it's reactor but soon found that it will take hours to overload thanks to the many new technology in corporated.
He cant wait that long nor will the enemy, but suddenly a though came to him a and he immdeatly started up the slipspace drive.
He was not trying to escape but in stead thought of how to destroy the ship.
The covenant super carrier was destroyed with a slipspace drive and now he tries to recreat it, besides as far as he knows silpspace and gravity don't mix well.
As for cordinates he just randomly typed in, it's not like it'll matter any ways as the portal will atomized everthing it touches.
"well then this it how it ends" he said before pressing the button.
Soon familiar black portal apears and sucked in the ship.
Thinking that this was the end he closed his eyes, little did he know that the portal will send him to another universe of eternal war.
Maybe it's because of the new slipspace drive or maybe bacuse he opened it deep in the planet or maybe he randomly typed in right cordinates or any combinations above but one thing is for certain is that he is not on reach anymore.
He opens his eyes and found that he is now staring in to space.
Literally!
It took him a moment for his spartan taining to kicked in and snaped him out of it.
He soon tap on the monitor and scanned the star systems but came back with nothing.
Even though he's in a parrallel universe but it doesn't mean that every thing will be same.
It had long branched of a long time ago resulting in a whole different out come.
Maybe it started out small, like a paticle more present during the beginning of the universe but 'a flap from a butterflys wings can cause a tornado on the other side of the world'.
well it doesn't matter what change because it changed and lead through another out come.
Well reguardless he is now alone in an unfamiliar universe.
- END -
I'm not very familiar with 40k lore so there will be some mistake, most of my knowlage came from the games like dawn of war.
Well the imperium is vast so anything can happened.
Now a little spoiler, he is going be a Rouge Trader, building an empire on the frontier.