Quick Author's Note: My knowledge of these two universes is rather limited, having played the majority of the Halo games and none of the Mass Effect games, and I am not the best writer, however I will do my best and I hope this story ends up as something resembling OK. Also some statistics are different from the official ones simply because I want them to be. Same applies to timing: I know it goes really quickly but hey, my story my rules. Also this will be told primarily from the Halo universe's perspective. Halo will also drastically outmatch Mass Effect. Deal with it.
Disclaimer: I don't even own copies of these great games so what do you think are the chances that I own the Mass Effect and Halo franchises?
Chapter 1: Timeline and Introduction
2553: The Human-Covenant War officially ends with the UNSC and the Covenant Separatists as the victors. The Sangheili and UNSC form an alliance. The former Covenant is fractured, becoming little more than pirates and raiders, and are completely disorganised. Admiral Alexander Frederick Halsey is confirmed KIA with his vessel, the Majestic Night.
2554: Intel indicates that the Covenant is reforming, with the various groups seeming to unite under one banner. The Sangheili and UNSC respond by preparing to defend against a possible resurgent Covenant. Captain Christina Jessica Cole, daughter of the deceased Admiral Preston Cole, marries Captain Philip Jonathan Whyte.
2555: The so-called New Covenant initiates the New Covenant War by attacking a human colony called Kortan. They are driven off by the timely arrival of Rtas 'Vadum's fleet. Due to the unprovoked intervention of the Sangheili, the majority of the xenophobia against them dissipates. Over the next few months, the New Covenant War is fought, albeit primarily in New Covenant space.
2556: The New Covenant War continues into the early months of the year, until the New Covenant capital is discovered with the aid of the newly allied Mgalekgolo. Upon the execution of their leader, the Prophet of Vengeance, the New Covenant splinters. The UNSC and the Sangheili decide to form a united government and invite the Mgalekgolo to join. Together, they found the Confederacy of Unified Free Species (led by a senate). The CUFS capital is a new cooperatively created colony called Unity. The glassing of a planet is declared a War Crime by the CUFS.
2557: The Unggoy and Huragok request to join the CUFS. After a month of deliberation, the senate votes in favour of this and so the Unggoy and Huragok join the Confederacy. Construction of a new cooperatively designed class of vessels begins. It has been christened the Alliance-class Super Dreadnought. At 40.3 kilometers, it is the largest ship class ever conceived by any member race. All SPARTAN-IIs and SPARTAN-IIIs are posthumously promoted to Commander Grade 2 (or SPARTAN Commander), a unique rank exclusive to them. The only non-SPARTAN given that rank is Franklin Mendez.
2558: The Ark is rediscovered, intact. Upon cautious exploration and examination, it is found to be devoid of the Flood and Sentinels. Colonisation begins and the Ark is declared the capital of the CUFS. The separate militaries are reformed into the Confederacy of Unified Free Species Armed Forces, led by Armed Forces Command (or AFComm). The AFComm Council are the twelve highest ranked officers in CUFSAF: five Admirals, five General Field Marshals, the head of Confederacy of Unified Free Systems Intelligence (CUFSI) and the Supreme Commander (currently Lord Terrence Hood). The remains of Onyx are discovered and investigated. The Dyson Sphere is discovered and explored. Exploration teams found Doctor Catherine Halsey, Commander Second Grade Franklin Mendez, Fred-104, Kelly-087, Linda-058, Tom-B292, Lucy-B091, Ash-G099, Olivia-G175 and Mark-G146.
2559: An artificial planet is discovered. Examination shows it to be an enormous Forerunner archive known as the Archive. Doctor Catherine Halsey is placed in charge, becoming the first so-called Head Archivist. The SPARTAN-IV Project is launched, using 16 year olds. Mendez and the surviving SPARTANs are to be their trainers. The entire CUFSAF fleet begins to be recalled and refitted with new weapons, armour and technology. The plan is for all shields to be greatly improved, more weapons to be added and the majority of ships to be fitted with at least one of the new MAC. A Halo Ring is discovered and explored. Upon discovery that it is untouched by the Flood, colonisation begins. The Index is moved to the Ark to be secured, the Control Room is secured and a so-called regional Armed Forces command centre is created. Its purpose is to monitor the surrounding region (designated as the Halo's effective radius), making it easier for the Armed Forces to respond to the continuing threat of former Covenant as orders do not need to come all the way from the Ark.
2560s: Over the next few years, the CUFS continues to expand and strengthen. The remainder of the Halo Array (including a new Installation 04 and repaired Installation 05) is found, secured and colonised, with regional Armed Forces command centres on each. The "CORTANA Contingency" is created and is used to refer to an outbreak of the Flood. During one such incident in the presence of Lord Hood, he orders the planet in question glassed. Upon consideration, the AFComm Council determines a set of scenarios where glassing is an acceptable action. This is called the "Hood Protocol" in honour of Lord Hood, who retires a few months later. The new CUFSAF Supreme Commander is a Sangheili called Fazn 'Teral. After a particularly vicious Covenant attack, the Colony Defence Act is passed. It requires that each colony have at least one Orbital Defence Platform in orbit. By the end of the decade the majority of the galaxy has been explored and, for the most part, colonised. However, some areas are still under Covenant control
2570: During browsing, Dr Halsey findsinformation in the Archive pertaining to something known as the "Intergalactic Tunnel". Upon investigation, it is discovered to be a perfect line between this galaxy and the next, an area where the usual spatial distortions, which exist in both realspace and slipspace, between galaxies are absent. This means that intergalactic travel is a possibility. It is decided that it will be explored at a later time and will be guarded until then. The first Alliance-class Super Dreadnought, the United Stand, is completed. It is placed under the command of Admiral Whyte, the main proponent behind the Alliance-class.
2571: The first class of SPARTAN-IVs graduate at age 28 with no casualties. The training of the next class is already well under way. The United Stand completes its maiden tour of CUFS space and moves on to active duty on the frontlines against the remainder of the Covenant. The CUFS senate votes for exploration of the other end of the Intergalactic Tunnel. Preparation begins for an expeditionary fleet to do so.
2572: A CUFS expeditionary fleet under escort from Admiral Whyte, the United Stand and approximately 2,000 other military vessels of all types leaves for the Intergalactic Tunnel. With top of the line Slipspace Drives installed, estimates indicate they should arrive in three days. This figure proves accurate, with the fleet arriving at the edge of the other galaxy on schedule. They discover a habitable planet in the first system they travel to and name it Horizon. (A/N: Original, huh?)
2573: Colonisation of the new system continues whilst other nearby systems are investigated. Numerous other worlds are found to be habitable and are colonised. Eventually, the CUFS finds a structure of unknown origin in one of the nearby systems. Some describe as looking like a giant blue tuning fork. Investigation begins under the guard of two frigates, the Dawn 'til Dusk and the Silent Lament…
Onboard the CUFS vessel Dawn 'til Dusk
"Captain, I-" began the Dawn 'til Dusk's AI, Aileen.
"Wait! This is important!" came the response.
Thirty seconds later, Captain George Campbell turned to the AI's avatar port. Captain Campbell was a relatively short, albeit well built, man with red hair that was showing signs of grey even with all the modern anti-aging developments. At 52, Campbell had lived approximately a quarter of the average expected lifespan. It was impossible to be sure, after all it hadn't been nearly 200 years yet so there was no way of knowing for sure but estimations indicated that 200 was to be expected in the future.
"What is so important that you have to interrupt me in the middle of a game of snooker?" he asked the AI with a scowl.
The figure of a beautiful young woman clad in jeans and a tank top reappeared on the port, rolling her eyes.
"Nothing major, just the research vessels reporting that they're going to try and turn on the device," Aileen deadpanned.
"Right then. To the bridge!" Campbell cried.
"Ever the dramatic…" Aileen muttered, shaking her head as she watched the captain run out of the room toward the bridge.
The group of marines in the room chuckled as they packed up the snooker balls before leaving to get ready in case they were needed.
"Anything happening yet?" Campbell asked as he rushed onto the bridge.
"Negative, Captain. They're just bringing it online now, sir," reported his communications officer, Johnson.
"Understood. Get me an open line with the research vessels and the Silent Lament. I want weapons online, just in case. Shields at maximum. Evacuate and lockdown all nonessential areas. Double time it!" Campbell barked out, receiving numerous affirmatives in return.
"They're bringing it online in 5… 4… 3… 2… 1… Activating," reported Johnson.
"Captain! Picking up massive energy readings from it!" reported Garun, his Sangheili sensors operator.
"Keep an eye-" started Campbell, before Garun cut him off.
"Energy spike! Massive one! What the…! Unknown vessels just appeared" Garun called out.
"Captain, it would appear that these vessels appeared with the energy spike. I hypothesize as a result that this is some form of long-range transportation device. Also, the vessels do not match any known designs and have no recognizable IFF," Aileen rattled off.
"So possible first contact? Int-" Campbell broke off as he saw the unknown vessels fire on the research vessels, obliterating two.
Taking a moment to look at them, Campbell noticed that they resembled over sized fighters with a slight resemblance to a bird. The spinal cannon seemed small but had torn apart the research vessels. There were five of them, one larger than the others, obviously the lead ship.
"Return fire! Weapons free! Hit 'em hard, ladies and gentlemen!" Campbell bellowed, reaching for the intercom.
"All hands, man your battle stations! This is not a drill! Repeat, battle stations! We are under fire! This is not a drill!" Campbell's voice blared across the speakers throughout the ship.
The Dawn began repositioning itself, lining up a shot on one of the smaller vessels. On her port side, the Lament was doing the same.
"MAC locked, firing in 3… 2…1… Firing!" the ship shaking as Aileen finished her countdown.
The MAC round streak toward its target on the far right of the enemy formation. What happened next caught all who saw it off guard. The MAC round passed clean through, gutting the vessel from prow to stern, tearing through some form of shielding on its way. Seconds later, a round from the Lament did the same to the leftmost vessel in their formation.
Evidently recovering from their shock, the other vessels opened fire, main guns targeting the Dawn. Unable to manoeuvre, the Dawn took all three shots to her prow, shields flaring.
"Damage report!" Campbell demanded.
"Shields down 0.3%, Captain. No hull damage at all," Aileen's voice spoke up.
"Y-y-your joking right?" Campbell stuttered, astonished.
"I don't joke during a combat scenario, Captain. Shields regenerated," Aileen replied.
"Like taking candy from a baby," Summers the navigator chuckled.
"Fire the MAC again. And tell the Lament not to use anything else, keep our true combat prowess hidden," Campbell ordered, grinning.
With that, the Dawn shook as its MAC fired into the right vessel, once again gutting it. The Lament's MAC followed suit, destroying the remaining smaller vessel. The remaining ship turned and retreated toward the artefact. Upon approach, it was surrounded by blue light before disappearing.
"Captain, before they fled, I managed to hack their vessel's mainframe. It appears the species is called Turians. They provide the main military strength for the interspecies government they are a part of," Aileen recited, evidently proud of herself.
"Good. I'll head to my quarters, meet me there, tell me what you can and we'll add it to the report. And get me a vidcom line with Captain Naras, we might as well submit a joint report," Campbell ordered as he turned to leave the bridge.
'This just got a helluva lot more interesting,' Campbell thought to himself.