City advantage, Fallen Leadership crumbled
- "The House of Devils is back. And they're digging into old Golden Age research labs across the system. This isn't a simple smash-and-grab. They're on a mission. At first, the Vanguard wasn't particularly concerned. At least, not in the Devils decided to move back into the Cosmodrome. Now the Devils are shifting a massive amount of resources to an area that's been dark for centuries. Normally, I'd say it's just another day. Except what's really got everyone talking is that Lord Saladin has left his post at the Iron Banner to take charge of the situation personally."
- — Ghost highlighting the start of the Crisis
The SIVA Crisis was a major conflict being fought between the SIVA-infected Fallen and the new Iron Lords. The crisis was triggered when the Fallen Splicers rediscovered SIVA within the long-sealed Plaguelands. While the orthodox leadership of the Splicers saw SIVA as another technology to be worshiped, the sect loyal to the House of Devils was more ambitious: they sought to use SIVA to make themselves into gods. Imbuing themselves with SIVA's power, the Devil Splicers began subsuming the rest of their House and spreading the techno-plague. Recognizing the ancient threat his fellow Iron Lords had sealed away long ago, Lord Saladin Forge issued a call-to-arms to the Guardians in order to raise a new generation of Iron Lords.
Prelude: Transmission Crisis
The Owl Sector reconvened for the first time since an event called the Dawn Calamity in response to field reports from Guardians whose armor had become infested with "tech mites", which manifested as swarms of colorful specks that swirled around their heads. Five varieties of tech mite were documented, each with a unique coloration: Brilliance 3.2 (green), Glory 2.1 (white), Splendor 2.6 (yellow), Magnificence 2.0 (blue), and Fortitude 3.1 (pink). The tech mites originated from the Dust Palace on Mars, but rapidly spread to other Guardians. While this phenomenon, designated "Transmission", initially alarmed the Vanguard as it overrode Guardians' armor systems, Guardians responded to it with enthusiasm and mocked attempts by the Owl Sector to quarantine them.
Unable to contain the mites' spread among the Guardians, the Owl Sector and Vanguard instead implemented a quarantine on the Last City in order to prevent non-Guardians' exposure. Meanwhile, Bypass Authority Berriole traveled to the Dust Palace to learn the origin of the tech mites. She followed sets of tracks to a lab, where various locked storage cabinets had been cut or blasted open. At a console in the lab, she discovered the mites were linked to a Clovis Bray project overseen by a Dr. Zarin Shirazi who worked under Dr. Willa Bray. Berriole transmitted records of Dr. Shirazi's experiments with the mites, which had been encrypted to an unusual degree, to the Owl Sector. The records revealed that the tech mites were a nanomachine therapy to improve subjects' intelligence and strength for the Golden Age's colonization effort, but they produced several unforeseen side-effects including manic and paranoid behavior, loss of voice, levitation, and comas. Shirazi developed a countermeasure and saved the test subjects, but she had become disillusioned with the project and recommended to Dr. Bray that it be abandoned.
Eventually, a third of all Guardians became affected by at least one variety of tech mite, prompting the Vanguard to further tighten the City's quarantine. The Owl Sector's Liaison to the Vanguard, Shun Li, accidentally became exposed to a sample of tech mites and lost consciousness soon after, forcing his fellow operative Ramos to take on the duties of Acting Liaison. Fortunately, the countermeasure was discovered among Shirazi's records, and the combined efforts of the Owl Sector's research corps, the Hidden, and the Techeuns succeeded in replicating it. Shun was revived, and the cure was administered to the Guardians, much to their disappointment. With the crisis ended, the Owl Sector was returned to standby status.
After sealing Shirazi's lab, however, Berriole noticed that the tracks that led to the lab appeared to have been made by Fallen, implying that a group of Fallen, possibly the Splicers, were responsible for the entire incident.
Raid on Felwinter Peak
- "The Iron Temple was once a place of Light. Then the Iron Lords were lost, and Saladin turned it into a memorial. Now it will be reborn, much like that curious servitor."
- — Tyra Karn.
At some point during the beginning sequences of the SIVA Crisis, the Fallen raided the abandoned Vostok Observatory under the command of Sepiks Perfected, the reconstituted remnants of Sepiks Prime. Unable to respond to the incursion before the Fallen completely overran the Iron Temple, Lord Saladin summoned the Guardians to help him hold off the Fallen until he arrived with additional forces. Fighting the Fallen through the mountains blistering cold, the Guardian reached the Observatory just as Sepiks arrived and began attacking the Temple. Using the high-ground to their advantage, the Guardian was able to drive the Fallen away and seemingly destroy Sepiks Perfected.
Upon the Guardian's success, Saladin arrived and finished off any cloaked Fallen. Unfortunately, the victory was bittersweet as Sepiks revives itself and flees. Having been ordered to track Sepiks escape, Shiro-4 detects several breaches on the Cosmodrome wall, prompting Saladin to send the Guardian to track Sepiks down.
The Cosmodrome Breach
As tasked by Saladin to investigate the breach in the Cosmodrome and to confirm Saladin's fears, the Guardian arrives at the wall and finds a section of it in ruins with a heavy Devils presence. Tracking Sepkis, the Guardian fights through the wall and finds a strange pattern outside and with Ghost scans, discovers that a nanotechnology is consuming the building, thereby confirming Saladin's fears that SIVA has returned. Instantly, Hive ships appear, apparently driven out of their holds by the Fallen. Fighting both Hive and Fallen to a sensor grid to restore the sensor network for Shiro-4, the Guardian encounters a new enemy of Fallen: The Devil Splicers. After defeating the new powerfully-augmented Fallen, Saladin now knows for sure that the Fallen have restarted production of SIVA for their own desires. Shiro-4 tracks to Fallen to the Plaguelands, an area that has been quarantined for years, but has now become the Devil Splicers territory.
To open up a new front for the war and to establish a beachhead in the Plaguelands, Saladin and Shiro have the Guardian infiltrate Splicer defenses for reinforcements but find that the Splicers have repaired a gun emplacement that was destroyed during the Collapse using SIVA. Any reinforcements would be destroyed but thanks to the Guardians efforts, they destroyed the SIVA nodes powering the cannons, allowing reinforcements to arrive and Guardians to explore the quarantined zone.
- "The Young Wolf has stopped the flow of SIVA to the Devil Splicers, ended the torment of the Iron Lords, and lifted centuries of grief and regret from Saladin’s shoulders. My old friend is a changed man. Centuries ago, I thought the story of the Iron Lords was finished. I see now that it was waiting for the next chapter."
- — Tyra Karn.
After returning to the Iron Temple to learn the full history of SIVA and the fall of the Iron Lords, the Guardian and Saladin agree that SIVA is still new to the Fallen and therefore haven't mastered it yet. Regardless, both wonder how the Fallen discovered SIVA in the first place. With Tyra Karn's help they follow a trail left behind by Lord Timur who was obsessed with the works of Clovis Bray, the original creators of SIVA. The trail led to Mars, deep in Cabal territory. With the Cabal nearby, the Fallen couldn't learn all of SIVA but after fighting through the Cabal, the Guardian was able to reach the lab where the SIVA prototypes were located, hopefully to find a solution to SIVA. The solution turned out to be a self-destruct sequence.
After retrieving the SIVA prototypes from the Clovis Bray lab on Mars, Shiro and Lord Saladin task the Guardian to go into Site 6 and destroy the SIVA replication chamber to end the SIVA Crisis. After fighting through the Fallen in the Archon's Keep and cutting off their control of SIVA, the Guardian enters into the Site 6 deep beneath the Warrens. Once the Guardian enters the replication complex, the Guardian finds the remnants of the Iron Lords that died during the attack on Site 6 in the Dark Age and are being controlled by SIVA. Once the remnants were defeated using a discarded Iron Battle Axe, thus putting the Iron Lords to rest, the SIVA self-destruct sequence is initiated and the Guardian successfully escapes, preventing any more SIVA from being created.
From the chaos of the battle, the Guardian recovered the lost battered helmet of Jolder and returned it to Saladin, granting him peace. For the Guardian's heroism and relieving centuries of burden, Saladin grants the Guardian The Young Wolf's Howl sword. With this, Saladin names the Guardian the first of a new generation of Iron Lords.
- "The Splicers are playing god. They view SIVA as a means to reshape how they see fit. The Hive are just victims of the Splicers' willingness to push their curiosity."
- — Shiro-4.
During the Guardian's patrols in the Plaguelands, the Guardian discovered that the Devil Splicers were engaging in all-out war with the Hive. Seeking to discover what was driving the Hive on the warpath, the Guardian began to search Splicer cargo and found that the Splicers have been corralling Hive Thralls on orders from an unknown Splicer Priest, for unknown reasons. Further investigation found that the Devil Splicers have been experimenting on the Hive using SIVA, explaining the Hive's violent aggression. Yet the news worries Shiro, as he initially believes that the Splicers are seeking to control the Hive using SIVA.
Seeking to end the Splicers' vile experiments by eliminating its leading figure, the Guardians form a fireteam and invade a Hive nest in an old missile silo currently being contested over with the Splicers. Fighting to the center of the nest the fireteam find an Ogre, Kovik's Monster, that was recently experimented on yet still alive. Soon the Splicer leader, Kovik, Splicer Priest, appeared with a rifle powered by the Ogre's Void eye. Despite Kovik's weapon and freeing the Ogre, the Priest was killed, ending the Splicers' experiments on the Hive. However, Shiro worries whether the Splicers will continue Kovik's work or not and wonders what other perversions the Fallen are conducting.
To further prevent the Devil Splicers from creating other monsters or weapons out of the Hive, Shiro-4 orders the Guardian to invade the Hellmouth on the Moon and stop the Splicers from abducting any more Hive Ogres. Fighting though both Fallen and Hive, the Guardian reaches the Summoning Pits right before the Splicers capture a Hive Abomination. Despite the struggle of facing the Abomination, the Hive and the Devil Splicers, the Guardian was able to slay the monster and therefore prevent the Splicers from gaining any more test subjects.
Breaking the Devil Splicers
The SIVA Crisis was not fully averted though, since any remaining SIVA was still out there and in Fallen hands, not to mention the Splicers' latest Archon was still alive, Aksis, Archon Prime inside his Perfection Complex and Sepiks Perfected was still in hiding since the Iron Temple raid.
Since the Devil Splicers proved SIVA's worth by bringing back Sepiks Prime, the Guardians under Shiro's orders, sought to end the "perfected" Prime Servitor, this time for good. Following the same path to the same lair where Sepiks Prime was destroyed, the Guardians fight to the Devils' Lair where Sepiks Perfected was being tended to. Killing the Captains protecting it, the Guardians were able to leave Sepiks Prime vulnerable to attack, and were able to destroy it. Much like what happened two years ago, Sepiks was killed, only this time for good.
After dealing with Sepiks, the Guardians were ordered by Shiro to infiltrate the Devil Splicers' true lair and end the radical group. After defeating Vosik, the Archpriest, repairing the Siege Engine and defeating Meksis, Siege Engineer, the Guardians infiltrated the SIVA Server Farm and descended into the Perfection Complex, where the true source of SIVA and the Devil Splicer threat resided. There, after a long and perilous struggle, the Guardians faced and destroyed Aksis using his own SIVA Charges and Empowerment. With the death of Aksis and Sepiks, the Guardians were able to successfully break the Devil Splicers' leadership.
During the attack on the Devil Splicers' lair, five mysterious monitors were activated. These five monitors unlocked a laser grid barring access to a SIVA engine. After Shiro-4 saw the engine, he told a fireteam to go solve the patterns on the SIVA Engine while it was normal, charged, and unstable. After solving the patterns, the engine turned out to be the Outbreak Prime, an Exotic Pulse Rifle.
- "Variks has brought unsettling news. The Devil Splicers have used SIVA to resurrect an old foe: Taniks the Scarred has become Taniks Perfected."
- — Commander Zavala
After a few months since the loss of their Archon, some of the Devil Splicers sought out allies to hopefully turn the tide of the Crisis. Those allies turned out to be the crew of the infamous Fallen Mercenary Taniks, the Scarred. To secure an alliance, the Devil Splicers used SIVA to resurrect their leader as Taniks Perfected. Though his mind and body are overtaken by SIVA, Taniks' leadership and ruthlessness remained. However, chatter of their alliance was intercepted by Variks, the Loyal who relayed his findings to the Vanguard.
Following the same path to Taniks' ship, the Guardians fight past both Hive and Splicer to board the Ketch. Chasing Taniks, through his ship as before, the Guardians corner him in the command station. Despite his resurrected body, SIVA upgrades and his varied weapons, Taniks was once again killed, leaving Taniks' crew and the Splicers in a desperate and severely weakened state again.
Aftermath and Retreat
With the complete loss of their leadership and constant attacks from the Guardians, the Devil Splicers made a complete withdrawal from Old Russia. While making their retreat, some of the Splicers were attacked by the House of Kings, frightening them. As a team of Guardians observed them, they noticed that the Devil Splicers weren't the only group of Fallen making a retreat, as the Devils, House of Winter, House of Exile and House of Wolves, all abandoned their hideouts.
This withdrawal led the Vanguard to believe the war with the Devil Splicers and with the Fallen as a whole to be won. That is, until the onset of the Red War, where the newly emerged yet mysterious House of Dusk continue the battle with the Guardians.