Rumbling

"While we saw the rise of weapons more powerful than Titans in the last war... we will never see a weapon that can stop the advance of millions of Colossus Titans. If the Walls walk even a single time... there will be nothing left we can do. All that can remain for humanity would be to flee in terror at the rumble of the footsteps that signal our end. These massive creatures would trample our cities, our societies... They would crush the flora and fauna in every ecosystem. They would literally flatten our world."

- Willy Tybur explains the destructive potential of the Rumbling to his audience during the Liberio festival

The Rumbling (地鳴らし) was a cataclysmic event involving Karl Fritz's Wall Titans marching across the earth, destroying all life upon it. For over a century, it was a key deterrence factor for the Subjects of Ymir on Paradis Island until the year 854 when Eren Yeager unhardened the Walls, freed the Wall Titans, and began the Rumbling.

Over the course of four days after first setting foot on the continental mainland, the Rumbling brought about the complete destruction of the northern continent of Marley along with significant devastation in the southern continent and neighboring nations. Approximately 80% of all human life on the planet was ended by the time the Rumbling was stopped prematurely by the combined efforts of the Marley's Warrior Unit and defectors from Paradis Island's Survey Corps.

Karl Fritz's ultimatum
During the final days of the Great Titan War between Marley and the Eldian Empire, King Karl Fritz used the power of the Founding Titan to raise three Walls on Paradis Island: Maria, Rose, and Sheena, each named for the three daughters of Ymir Fritz. These Walls were constructed from the hardened flesh of countless Colossus Titans created with the Founding Titan's power.

Upon gathering the remnants of the Eldian Empire into the Walls and closing the gates to the outside world, Karl Fritz issued one final declaration which assured the enemies of Eldia that if Paradis were to come under attack, the Founding Titan would unleash the Wall Titans to trample the earth into ruin. However, Karl Fritz secretly confided with the Tybur family and the remaining Fritz family on the mainland that this ultimatum was an empty threat of deterrence. In truth, Karl Fritz made a "vow renouncing war" with the Founding Titan ensuring that none of his successors would use the Founding Titan to threaten the world again, allowing for Eldia to live in a brief paradise before their enemies would arrive to destroy Eldia as Karl Fritz believed they deserved to be.

As Karl Fritz had hoped, no open declaration of war or act of aggression was made against the people of the Walls for over a century, though Marley would use the lands beyond the Walls on Paradis Island as a penal colony for criminal or undesirable Subjects of Ymir transformed into Pure Titans. However, over eighty years after the end of the Great Titan War, Marley's declining military industry turned the nation's attention towards Paradis and the fossil fuels hidden beneath Eldian lands. Despite the vow renouncing war being known to Marley through the Tybur family, the threat of the Rumbling was too great a risk to attempt a full-scale invasion. Instead, Marley began training the Warrior Unit in preparation for the Paradis Island Operation, an infiltration of the Walls with the power of the Titans that would not provoke the attention of the King of the Walls with military force. Likewise, the Eldian Restorationists led at this time by Grisha Yeager attempted to use this Warrior program to infiltrate the Walls in the same fashion in order to steal the Founding Titan to restore Eldia.

In the year 845, the power of the Attack Titan caused Grisha Yeager to inherit future memories from his son Eren, revealing the Fall of Wall Maria later that day. Grisha fled to the chapel of the Reiss family where he was influenced by the will of Eren in the distant future to steal the power of the Founding Titan and slaughter the Reiss family. The future memories of the Attack Titan revealed to Grisha the sight of the Rumbling that Eren would create.

While spying on the Eldians within the Walls before his entry into 104th Training Corps, Reiner Braun reminded himself and his fellow Warriors Bertolt Hoover and Annie Leonhart that the threat of the Rumbling and the fate of all humanity depended upon the success of their mission.

Truths rediscovered
During the Survey Corps's attempt to capture Annie Leonhart, a portion of Wall Sheena in Stohess District was damaged by Annie's Female Titan, revealing the face of a Wall Titan within it. This revelation caused great confusion among the Survey Corps and panic in Minister Nick of the Church of the Walls, demanding the Corps to cover the face of the Titan before sunlight could reach it. The presence of the Titan in Wall Sheena led Squad Leader Hange Zoë to quickly deduce that all of the Walls must contain Titans within them. This created unease among soldiers such as Armin Arlert, who wondered at the possibility of all Titans within the Walls emerging to walk.

Upon discovering the journals of Grisha Yeager in the Yeager family's basement in Shiganshina District, the Survey Corps learned of the nature of the Rumbling as a deterrence factor that had kept enemies of Eldia away from Paradis Island for over a century until five years ago. During a gathering to discuss the findings of Grisha's journals, the leaders of the military in the Walls discussed how the power of the Founding Titan to release the Wall Titans may be achieved despite the vow renouncing war. Recalling his encounter with a Titan whom he later realized was Dina Fritz, Eren Yeager realized he could still bring out the Founding Titan's power despite his non-royal blood as long as he was in contact with a royal-blooded Titan, though he kept this realization to himself for the sake of Queen Historia Reiss.

Memories of the future
During a ceremony honoring the survivors of the Battle of Shiganshina District, a moment of contact between Eren and Historia opened a glimpse into Eren's future memories where he saw himself influencing the decision of his father Grisha in stealing the power of the Founding Titan and slaughtering the Reiss family. At this time, Eren saw the sight of the Rumbling that he would cause in the future and his inevitable defeat after annihilating eighty percent of all human life.

One year after the medal ceremony, Paradis Island was visited by the Anti-Marleyan Volunteers, a secret organization of Marleyan soldiers led by Yelena, all foreign conscripts who wished to aid Eldia against Marley with the help of Zeke Yeager. Through the Volunteers, Zeke proposed cooperation with Paradis to bring him into contact with his half-brother Eren Yeager to begin a small-scale Rumbling which would further deter enemy attacks until Paradis could reach a point of technological advancement sufficient enough to no longer rely on the power of the Titans for protection. While the various military leaders of Paradis were openly against cooperation with Zeke, a former enemy, Eren revealed his discovery of a royal-blooded Titan acting as a potential loophole for the Founding Titan's power, thus making the Rumbling a possibility for Paradis to use in self-defense.

One year later, the Volunteers introduced the leadership of Paradis to Kiyomi Azumabito, ambassador from Hizuru and ally of Zeke. When discussing the requirements to make Eldia a self-sustaining nation on Paradis Island, Kiyomi proposed the use of the Rumbling as deterrence for at least a period of 50 years while Paradis caught up technologically with contemporary nations. Despite his foresight of the Rumbling, Eren refused to comply with Zeke's plan to use the Rumbling and pass his Beast Titan to Queen Historia to ensure the perpetuity of the process, deciding instead to pursue diplomatic solutions for Paradis. Regardless, the Rumbling would become a key factor in the military alliance between Eldia and Hizuru.

The following year, Hizuru's trade proposals for Paradis Island failed, once again leaving them with only the Rumbling as deterrence. As one final alternative, the Survey Corps made plans to embark on an undercover survey to Marley in order to gauge global sentiments towards Eldia for themselves. At this time, Eren was approached by Yelena regarding Zeke Yeager's true plan to euthanize the Subjects of Ymir and bring about a peaceful end to Eldia's suffering. Anticipating the failure of the Survey Corps's attempts to make peace with Marley, Eren made plans to cooperate with Zeke Yeager long enough for him to achieve the inevitable Rumbling. Eren confided in Floch Forster regarding his true goal of wiping out all life beyond Paradis Island with the full strength of the Wall Titans. Agreeing upon a small-scale Rumbling following the euthanasia plan, Yelena recommended Port Karifa in northern Marley as a primary target to cripple the navies of Paradis Island's enemies, though she expressed concern over potential advancements in aerial technology being researched in Fort Salta to the far south.

Upon arriving in Marley, Eren had begun to lament the unfathomable loss of life he would soon cause. Despite public favor increasing for Subjects of Ymir worldwide, Paradis Island remained a point of high hostility at this time, causing Eren to lose all hope in changing his future. He then abandoned the Survey Corps in order to pursue his own agenda.

Marley's preparations
After the conclusion of the Marley Mid-East War, Willy Tybur was recruited by Zeke Yeager to announce to the world the threat that Paradis Island posed in order to remove global hostility towards the Subjects of Ymir as a whole. During his speech before the international ambassadors and journalists, Willy reminded the audience of the many Wall Titans present on the island and the possibility of Eren Yeager unleashing these Titans upon the world. In order to prevent this apocalypse from occurring, Willy Tybur urged the leaders of the world to unite against Paradis in open war.

Shortly after Eren escaped imprisonment on Paradis Island for his desertion, Marley launched an assault upon Shiganshina District in revenge for Liberio in order to take the Founding Titan from Eren. When Zeke arrived upon the battlefield, Marleyan forces desperately tried to prevent Zeke and Eren from coming into contact and unleashing the Wall Titans. After learning of Zeke's true plan to use the Founding Titan to sterilize the Subjects of Ymir, Armin speculated on Eren's true motivation for conspiring with Zeke. Deducing that Eren would instead use the Founding Titan to unleash the Titans in Shiganshina's Walls, Armin trusted that Eren was on their side.

The Walls fall
When Eren and Zeke came into contact, an instantaneous moment in time occured where Eren came to understand that Zeke's will as a descendant of the royal family superseded his own will as the Founder's carrier. Eren learned that the Founding Titan's power was dependent on the will of Ymir Fritz, forever enslaved to obey the will of the royal family who enslaved her in life 2,000 years ago. When Ymir prepared to carry out Zeke's will to sterilize the Subjects of Ymir, Eren urged her to reject her duties and act in her own will. In this moment of contact with his founder, Eren saw into the mind of Ymir and recognized despite the horrors the ancient King of Eldia subjected her to, she loved him in such a way as to bind her actions to the will of his line forever. Despite this, Eren foresaw that Mikasa Ackerman's actions would have a profound effect on the will of Ymir and would bring about the end of the Power of the Titans.

Choosing to act in Eren's will, Ymir lent the power of the Founding Titan unto Eren who then unhardened all the Walls on Paradis Island. With the full power of the Founding Titan, Eren telepathically declared his will to all Subjects of Ymir that he had unleashed the Wall Titans upon the world to crush all life beyond Paradis Island. Eren then led the Colossus Titans on a southward march, unhindered by the Marleyan and Eldian soldiers preoccupied with Zeke's Titans throughout the city.

After several days, the last of the Wall Titans began to leave Eldian territory on Paradis Island. By this time, the remaining Marleyan Warriors on the island joined forces with Eren's former friends in an attempt to pursue him and stop the Rumbling. While the allied soldiers were left to confront Floch Forster and the Yeagerists guarding Paradis Island's port, Eren and the Colossus Titans approached the Marleyan mainland, crossing the sea by swimming. Commander Hange Zoë estimated that in the half a day it would take to prepare the Azumabito family's flying boat to pursue Eren, the Rumbling would have already destroyed up to inland, the entire continent to follow in as few as four days.

Arrival on the mainland
While the allied soldiers were en route to Odiha, Eren made use of the Founding Titan to speak privately with those he knew were coming to stop his advance. While conversing with Armin, Eren revealed his foreknowledge of the Rumbling and its premature end, as well as the unknown role that Mikasa would play in ending the Power of the Titans. Likewise, Eren provided Mikasa with a vision of a world where he would have happily lived with her had she chosen to confess her true feelings for him. At the end of each conversation, Eren erased the memories of their individual meetings, though this memory erasure would prove unsuccessful and only temporary on Mikasa Ackerman.

At this time, the Rumbling arrived on the northeastern Marleyan coast, completely bypassing the fleet of the Global Alliance and shrugging off all artillery fire during their advance. Many civilians were left behind in the slaughter as the Marleyan military fled ahead of them without providing warning to the masses of the incoming Rumbling. The Titans advanced southward, trampling cities into ruin and climbing over mountain ranges to outpace the fleeing populations on the roads. During his genocide, Eren remained unfazed by the deaths of millions, seeing instead the sprawling sight of a free world ahead of him, the sight he had forever long for. Although the allied soldiers arrived in Odiha with enough time to adequately prepare the flying boat for flight, the Rumbling arrived at the city shortly before they were able to fuel the craft. To provide the engineers enough time to get the flying boat underway, Commander Hange stayed behind to kill the Titans closest to the hangar bay, appointing Armin Arlert to be the next Commander of the Survey Corps shortly before dying to the Titans' heat. As the soldiers flew from Odiha, the city was annihilated under the Titans' feet.

The Battle of Heaven and Earth
Any survivors of the Rumbling on the continental mainland of Marley regrouped at Fort Salta in the southern mountainous regions of the country. When the Founding Titan and the force of the Rumbling approached the fort, the Marleyan military sent out a fleet of airships to drop an arsenal of explosives on the Titans to halt their advance. While Marley made their final stand, the Titans began to advance into neighboring countries, pursuing fleeing civilians into the countryside and leaving none alive in their path. Despite their best efforts, Fort Salta's bombardment was largely ineffective, and the Founding Titan formed a husk of Zeke Yeager's Beast Titan to assault the airships, rapidly destroying Marley's last offensive. Not long afterwards, the flying boat arrived and deploys the Survey Corps soldiers alongside the Cart Titan and Armored Titan to halt Eren's advance.

In an overwhelming counterattack, Ymir summoned dozens of forms resembling the Nine Titans of ages past all along the massive body of Eren's Founding Titan. The past Titans rushed the Warriors and the Survey Corps, quickly overpowering them while Commander Armin was caught and taken away towards the rear of Eren's Titan by one of the summoned forms resembling an okapi. Forced to retreat, the soldiers desperately evaded the constant rush of attacks from the Titans, and Captain Levi Ackerman was wounded in the battle. Before the Titans could kill the allied soldiers, Falco Grice's Jaw Titan arrived, utilizing bird-like traits gained through Zeke Yeager's spinal fluid to carry away the allied soldiers. The soldiers concluded that, in order to halt the Rumbling, they must kill Eren Yeager by any means necessary. Returning to Eren's Titan, the allies launched their own counterattack on the Titans.

While being consumed by the okapi Titan, Commander Armin met with Zeke Yeager, who had likewise been consumed some time earlier after his contact with Eren, within the paths. Desiring to end the tremendous loss of life brought on by the Rumbling, Zeke and Armin urged the souls of dead Titan inheritors they knew of in life to come to their aid. The Titan husks of Bertolt Hoover, Ymir, Porco Galliard, Marcel Galliard, Grisha Yeager, Eren Kruger, and Tom Ksaver are immediately taken control of by the past inheritors. At this time, Zeke Yeager emerged from the spine of the Founding Titan, alerting Captain Levi to kill him. After Zeke is decapitated, the Wall Titans halted their advance across the world. Jean Kirstein used explosives taken from the Yeagerists to decapitate the Founding Titan, unleashing the ancient anomaly responsible for the Power of the Titans. Freed from being consumed, Armin transformed into the Colossus Titan, utilizing its explosive transformation to destroy the body of the Founding Titan and the Titan husks.

Despite their efforts, the Titan anomaly put up a desperate defense, emitting a cloud of gas upon the refugees at Fort Salta, creating a horde of Titans to come to its aid as it grappled with the Armored, Female, and Cart Titans who struggled to prevent it from reuniting with Eren and resuming the Rumbling. Meanwhile, Eren Yeager transformed into a Colossus Titan to battle with Armin Arlert.

Recalling her vision of another life with Eren, Mikasa rejected Eren's wish for her to forget about him after his death. Choosing to forego a life with Eren over the necessity of ending his atrocities, Mikasa located Eren's head on the end of a long spine within the mouth of his Titan. Mikasa Ackerman severed Eren Yeager's head from the spine, bidding him farewell with a kiss. Upon seeing Mikasa's choice, Ymir abandoned her hold over the Founding Titan, ending both the Rumbling and the Power of the Titans forever.

Aftermath
Three years after the Battle of Heaven and Earth, the survivors of the battle embark to Paradis as ambassadors for Marley to begin peace negotiations with Paradis. As they sail for the island, they read a letter from Historia Reiss which explains that the remaining Yeagerists have formed an army to defend Paradis from the threat of the outside world.

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