Chapter 61: Underworld Rumbling
The inhabitants of Agreas did not notice the ground beginning to rumble. They, high in the sky of the Underworld, could not feel the vibration of the dirt.
But they saw the lightning.
Those near the edge of the flying city, with the enhanced eyes of devils, saw the yellow flash of lightning that fell from a clear sky. It was a curtain of electricity stretching from one side of the horizon to the other.
They heard the crash of thunder as the energy impacted the ground with a cacophonous boom.
It was the curious eyes of the civilians of Agreas that first saw the Titans.
They emerged from beyond the mountains, enormous beings of white flesh and bone.
Thousands of them.
Ten ranks deep and reaching across the horizon as far as a devil's eye could see, these giants stood sixty meters tall, bigger than most of the dragons Ratting Game fans saw occasionally.
As one, these colossal beings advanced toward the flying city.
They weren't moving quickly, but their sheer size meant they swallowed the distance at a rate that most couldn't outrun.
And where they passed, the Underworld burned.
The very air warped and hissed with the heat they radiated, setting the world aflame. Every step crushed stone, tree, and animal. Clouds of dust and ash rose as they marched, blackening the air above.
The ground was on fire, the sky darkened from the clouds of dust and ash, and a tide of white between the two.
And behind the wall of white Titans, the Attack Titan advanced.
Five times the size of the Colossal Titans, the... monster was a creature of white bone alone, only its head having any semblance of flesh.
A demented, deformed centipede-like creature only shaped like a man in the vaguest sense, its enormous bulk was supported by its ribs acting as legs.
Its head, attached to a sinuous spine, lulled over the advancing army. Long hair framed a horrific face, its eyes focused solely on the flying city.
Step by step, the Rumbling advanced, crushing the Underworld flat underfoot.
But the Underworld wasn't without its defenders.
Barely had the citizens of Agreas begun to feel fear at the approaching tide of destruction before a call from the city leaders rang out. The confused and frightened heard words of reassurance before they found themselves engulfed in an enormous teleportation spell.
Tens of thousands of devils found themselves confused and disoriented as they were displaced towards the outskirts of Lillith, the devil capital, where the non-combat staff of the Satans' various ministries tried to maintain some semblance of order.
Agreas was left almost entirely empty.
Almost.
From every corner of the flying city, devils of power emerged.
Lords and Ladies. Ultimate and high-class. Victors of the Rating Games and reincarnated devils of great power. Peerages of the Satans and Extra Devils.
Almost immediately, two camps formed.
It was a deviation from the plan, one caused by having way more defenders than the Satans had recruited, but one that very few bothered to complain about.
In case the Chaos Brigade tried to sneak members onto the nearly abandoned city, defenders needed to remain. To have the Great King faction take over that duty freed up more attackers.
There was also the fact that most could not say no to Zekram Beal.
Led by a Pawn of Leviathan, the attackers launched themselves at the oncoming tide of Titans.
Led by the Great King, the defenders remained on Agreas to protect the city from surprises.
The former went to battle.
The latter went to hunt, searching for the secret lab they had paid so much to locate.
One side chose to dive into danger, charging at a threat to their home and way of life.
One side chose the safety of the air, secure in the knowledge that the Rumbling was a problem only for those lesser beings who could not fly.
Mikasa Ackerman was the first devil to reach the white wall of bodies.
With instincts and training designed for this very purpose, no longer bound by the limits of ODM gear, the last scout faced down the nightmare of her youth.
It was different, yet the same.
These Titans were just as large and imposing and, in many ways, even more dangerous than the original Wall Titans had been.
The heat they radiated set the air ablaze, and their bodies exuded an aura that Mikasa could now identify as Touki.
Yet Mikasa wasn't the weak girl she had been either.
The first Titan died when two copies of Purgatorio were carved through the Touki like it wasn't even there.
It fell, crashing into the ground with a cacophonous impact and sending those behind it stumbling over its body.
Mikasa killed two more before the blades in her hands dissolved, their forms disappearing as the magic Yuuto had left in them ran its course.
She summoned two more.
These weapons, this Balance Breaker, were the closest she had found to the blades of her youth, and their unique holy/demonic abilities ensured that they could cut anything. Even Touki reinforced bone.
Every day, Mikasa worked with the Knight in combat and endurance.
In the pocket dimension Adjuka had created for her years ago, designed to work around her lack of magic to power her enchanted weapons, thousands of copies of Purgatorio waited to carve through Titan necks.
With her eyes locked onto the approaching Attack Titan, Mikasa had time to wonder why Eren had chosen to use the Warhammer to regain this form.
She had a guess.
If Mikasa had been alone, she probably would have charged right at it, trying to stop this as soon as possible.
But she wasn't alone.
Behind Mikasa, the devils bore down on the Titans.
So, Mikasa did not attack Eren directly.
Instead, she led.
An advanced scout, showing those behind her the path.
The next Colossal Titan fell under Mikasa's blades as she flew behind it, cleanly severing its spine with a movement she had practiced ten thousand times.
Then she was on to the next one. And the next. And the next.
Within seconds, thirteen more of the enormous humanoids had their spines severed and fell to the ground, creating a stumbling block for those behind them before they dissolved.
Mikasa grit her teen in frustration as the heat started getting to her.
Promoting to Rook would lessen the speed she gained from her Knight promotion. Perhaps a Queen might have been better, but she gained no benefit from the Bishop aspect, so she had decided to maximize her strengths rather than shore up her weaknesses.
Deciding discretion was the better part of valour, at least temporarily. Mikasa took to the air, climbing higher to escape the heat and cool off.
It let her get a good look at the battle.
Hundreds of devils were laying into the Titans, and the results were... mixed.
The simple fact was that most devils were simply not trained on how to fight Titans, let alone ones reinforced by Touki.
Most had been told to watch her for how it was supposed to be done.
They had noticed Mikasa's methods and tried to replicate them to the best of their abilities. They targeted heads with blasts of fire and force. Swordmen and women carved into legs, sending the giants falling to serve as a roadblock.
Yet the Titans just kept regenerating.
Severed legs regrew. Collapsed skulls expanded. Touki turned blows that would have been devastating into only shallow wounds that closed before they could be targeted again.
Titans simply did not die unless that small section of their spine was severed. It didn't matter if every other body part was destroyed if that one piece was still intact.
If the attack were off even a little bit, the Colossal Titan would regenerate far faster than would be possible without Eren's Senjutsu powering them.
It wasn't that they weren't having some success.
Grayfia Lucifuge had turned a kilometre's worth of Titans into ice statues. Even with the heat of the creatures radiating every second, the Strongest Queen kept a lock on hundreds of Colossals through her magic.
Diehauser Belial might be unable to use his clan trait, Worthlessness, on the Titans because they operated on a principle from another world, but he had faced Touki before. In front of the Emperor of the Rating Games, Titans lost their defences, leaving them as little more than big, hot humans. His Peerage tore through the squishy monsters.
Okita Souji had been Mikasa's sparing partner for years and was one of the few who managed to replicate her feet of targeting the napes of the neck, his body count already surpassing hers.
Beowulf had a smaller body count only because he was less precise, focusing more on carving through limbs than the precise work needed to put the Titans down for good.
Sutr II was revelling in the heat and fire the Titans gave off. Staying far away from Grayfia's part of the battlefield, he was a whirling inferno that burned the eyes to look at.
Tannin led a thunder of dragons to pass over the heads of the Titans in an air bombardment of fire and force, trying to target the spines.
All over the battlefield, the Underworld's greatest combatants pitted their full might against this new, more powerful Rumbling and held it back.
Then Eren started to fight back.
Mikasa saw it happen.
Saw the thousands of white Colossal Titans seem to flex, every muscle in their body shivering at once.
She knew what was coming, but her shout of warning was lost in the great bellow of steam that erupted from every single Titan.
It was not the explosion that accompanied the shifting of the Colossal Titan but rather the Colossal's ability to trade muscle mass for an outpouring of heat.
It was no less deadly.
An explosion of expanding superheated air erupted from the army of giants, frying those too close and fragile to defend themselves. Sutr II dove atop Okita and Mathers to wrap them in his enormous bulk to try and give them time for Mathers spell to defend them. Beowulf endured with a quickwitted promotion to Rook, giving him time to join his Peerage members.
Others weren't so lucky.
Devils were not immune to heat; they were just slightly more resistant to it than humans. The sudden onset of boiling steam took hundreds flatfooted, and dozens died, their skin blackening and blood boiling under the intense increase in temperature.
The attackers weren't idiots, though.
Like Mikasa, they took to the air on their wings, gaining a reprieve from the spike in heat and readying to lay into the Titans from the safety of on high.
It was here that Mikasa's instinctual hesitation to approach the Attack Titan was proved to be the right call.
Hundreds of smaller forms grew from every spike atop the enormous centipede-like Titan.
Shaped like long-limbed apes, they curled back their arms and let loose thousands of splinters of white bone, the smallest still bigger than a person's head.
Open and exposed in the air, the devils faced the bombardment as best they could.
Whether trying to dodge with speed, block with spells or simply tank the damage, they had more success than humans would have, but they still took casualties from those not quick enough or tough enough to endure.
Bodies fell from the sky like dying birds, but the majority of attackers remained to witness the next trick Eren had up his sleeve.
The wall of oncoming Titans reformed.
Those who were injured regenerated. The dead were resummoned. And those who expended muscle mass for the shockwave of steam regained their spent flesh.
Using Senjutsu and an enormous wellspring of power, Eren had turned the Rumbling from something modern-day humans could deal with into an unstoppable tide that even the strongest devils were struggling to survive.
The Rumbling continued to march forward. Relentlessly. Inexorably.
Crushing and burning the Underworld as it went, approaching Agreas with every second that passed.
But the Underworld was not out of tricks just yet.
There was a reason Agreas had been flying in this particular region, surrounded by mountains on all sides.
Falbium Asmodeus was not only a military strategist with few equals, but he excelled in defensive battles. When the most reclusive of the four Satans could be bothered to wake up, his mind was the equal of his friend, Adjuka, in his field of interest.
Though he might be locked down in a battle for his life against the strongest Longinus, Falbium still had days to set up the battlefield to his specifications, learning what he could from Mikasa's retelling of the Rumbling of her world.
The Titans descended the mountains, their footing already unstable from the uneven ground, and fell right into the trap of the devil army.
Tens of thousands of spells, each no stronger than what a human magician could use, set off at once.
For days, the legions of the military had been hard at work laying pits, rock slides, and other assorted traps to stop the march of the Titans from advancing close to the flying city.
The army was not made of high-class devils, baring a few captains here and there.
No, they were the rank-and-file, low and mid-class devils that comprised the vast majority of the population. These were not beings with unique bloodlines or great magic. Just men and women looking to do what they could to protect their homes.
Even a little pebble can set off an avalanche.
And there were a lot of pebbles Eren needed to crush if he wanted to stomp this world flat.
The first line of Titans fell on those pebbles, crashing into the ground with the deafening boom of bombs falling. The Colossal Titans in the second row tried to step onto or over their fallen brethren to continue their uncompromising march but found a second line of traps waiting.
It only took minutes for the entire advance to grind to a halt as the enormous bodies blocked their fellows.
More than the hundred or so Ultimate class beings, it was the countless soldiers who had toiled for days setting up fault lines, landslides, and mud pits large enough to trap a Titan that stopped the Rumbling.
These weak soldiers might not be able to kill Eren's army, protected with Touki, but they sure as hell could give their heavy hitters time to finish them off.
From the sky where they retreated, the spear of the Underworld descended upon their open targets, taking the opportunity to wreak devastation on the defenceless Titans.
They had learned from their first bout, attacking quickly and decisively before retreating to escape retaliation from the heat.
The Attack Titan was not inactive when facing this most recent setback.
The hundreds of Ape Titans lobbing fractured material were joined by equal numbers of Warhammer Titans equipped with projectile weapons. Spears, javelins, slings, and arrows were less numerous than the cluster shot projectiles, but each was targeted and much more powerful.
Most devils could not both attack and defend themselves simultaneously, so they took their distance from the Attack Titan to maximize their utility by aiding the army in slaying the Colossal Titans.
Even if Eren could continue to regenerate his ground-shaking army, every loss would divert his attention and sap just a bit more of his power, giving their own fighters a better chance at finishing him off for good.
And Mikasa had no intention of letting Eren take even one step closer to those she wanted to protect.
The ambush had ground the Rumbling to a halt, but it wouldn't be long before Eren simply decided to dismiss the fallen Titans and conjure more behind their lines.
Mikasa had minutes at best before this delay was overcome.
With a deep breath and a ghosting of her hand over the scarf at her neck for luck, Mikasa launched her own counter-attack, pulling a green cloak from her storage tool as she called out to her only Peer.
"Behemoth!"
High in the sky, way higher than Mikasa could have flown naturally and hidden behind the layers of smoke and dust, an enormous shadow blotted out the light of the Underworld's fake sun as Serafall Leviathan's only other Peerage member turned back into their original form.
The enormous beast, larger than even a Colossal Titan, fell onto Eren's back with all the might of a meteor.
Behemoth wasn't a being known for magic. Its demonic power was only high-class, yet it was still firmly considered an Ultimate-class devil for one reason alone.
Sheer, brutal, physical power.
The Attack Titan's spines could not hold it aloft under the impact of the sudden attack, and it smashed into the ground with yet more earthquake-level shocks.
Right away, all the summoned Titans on Eren's back turned their attention to the new arrival as the enormous beast, a demented cross between an elephant and hippo, bulldozed from the tail toward the front of this white centipede-like creature.
With a trumpeting bellow, Behemoth crashed through dozens of Titans, stones and weapons unable to so much as scratch their thick hide.
Like a stampeding elephant, the reincarnated devil bulldozed its way through a half-formed Colossal Titan, reaching the halfway point on Eren's back within moments and powering through with almost unstoppable momentum.
And met a wall of armour-clad Colossal Titans strung out between the two ridges of the Attack Titan's spine.
Behemouth's charge was halted after they failed to pierce more than two layers deep.
Halted and surrounded before they got close to the Titan's spine, Behemoth let out another trumpeting bellow and began to lay waste to the Titans around it, fighting to escape its imprisonment.
And to buy time and attention.
After days of planning and concocting scenarios, every single estimation the Satans, Azazel, and Mikasa had come to the same conclusion.
They couldn't win.
If Eren truly gained the power of the Infinite Dragon God, even if only a fraction, then not even all the Underworld's forces, including the Satans themselves, would be able to stand up to him if he decided to unleash it all at once.
If it weren't for his desire for the Malebranche to gain a more permanent power-up, Eren could have used the Warhammer to summon a Titan so large that the explosion would entirely destroy the Underworld.
No, one could not win against infinite power in a head-on-head collision.
Thankfully, though he had power, Eren only had a few ways to use it. So the Satans had concocted a plan that was, ideally, designed to circumvent the notion of a head-on collision entirely.
Eren needed a war to entice Malacoda so he wouldn't destroy everything in one blast. More than likely, his attack would come in a form he was familiar with, I.E., The Rumbling.
Its greatest ability wasn't in direct damage but in its grind. Its thorough and inevitable destruction of anything and everything under enormous feet.
Perfect for a battle-hungry sapient weapon.
The Underworld's struggle for survival would be Eren's sacrifice to the leader of the Malebranche.
And that was their salvation.
Eren needed a battle.
They'd give it to him.
And kill him while he was distracted.
There was just one problem.
Eren was a sage, and the Satans didn't know how poor his sensing abilities were. They thought he was the greatest sage ever to live. That fact had been pounded into their heads time and time again, so they had to find a way around his supposed abilities.
What do you know? They had a being with them who had no power to speak of. One that was intimately familiar with Eren, his methodologies, and killing Titans.
They had no idea what form Eren would take, but it stood to reason that it would be large. Either a Colossal Titan or something similar. So they had Behemouth waiting to distract it while everyone else halted the advance.
While Falbium had been preparing the battlefield, Sirzechs had been recruiting defenders, and Serafall was setting up the evacuation spell, Adjuka Beelzebub had only one job.
Create a device that could hide Ki from the greatest sage to ever live.
With her life force completely invisible, no other power to sense, and all the Attack Titan's eyes focusing on Behemoth, Mikasa landed on the long spinal column.
She didn't hesitate.
With no way of knowing where Eren was and a limited time before he conjured more titans who could see her, Mikasa drove two copies of Purgatorio deep into the neck of the Founding Titan.
It reacted instantly, white bone forming into a copy of the Jaw Titan, but Mikasa was already gone, trailing her blades along as she flew up closer to the head.
Closer to Eren's most likely location.
Devil wings carried her up along the bone road toward the head, slicing and cutting away at the thick, white material.
Mikasa prayed this would be enough.
That this would stop Eren.
That when he asked her if he could do it all again, he meant if she could stop him and not if she could live through the destruction of her world a second time.
Eren might not sense her, but he could feel the damage to his body and trace its route.
Warhammer Titans grew from the base of his skull, weapons poised to skewer her.
Only... their thrust went wide, missing her by meters.
Was Eren letting her get close? As she flowed under the spine, Mikasa wondered, blades still attached, and her wings carried her upside down.
Then, an enormous jaw burst from the underside of the neck and nearly swallowed her whole.
With the speed and decisiveness she had cultivated since she had first picked up that knife to fight, Mikasa abandoned her two blades and folded her wings. She fell, barely escaping the teeth of the Jaw Titan.
But its eyes didn't track her.
In fact, its head swivelled as if searching for something despite Mikasa being less than a meter from its face.
...The Colossal Titans hadn't reacted to her either, had they?
It wasn't that Eren was trying to let her kill him. Mikasa had almost been hit a few times by the garage from the Ape Titan.
It was that, for some reason, he really couldn't perceive her.
Whether it was because Eren was doing it deliberately or because Adjuka's device somehow made her invisible to him, Mikasa didn't waste the opportunity presented.
Mikasa plunged two more copies of Purgatorio into the spot right behind the Jaw Titan, leaving them there as it snapped at them instinctively.
And, with two more, she carved the last few meters toward the head of the Attack Titan.
Purgatorio's blades snapped as Eren increased the density of his Touki against this threat that he couldn't perceive.
Mikasa grit her teeth to choke a sob.
If Eren had been anywhere in the spine of the Warhammer-formed Titan, he would have died already.
That he wasn't meant he could only be in one place.
Two more blades of Purgatorio appeared in her hand.
Before Eren forced himself to trample another world.
So Eren didn't have to look into the eyes of another dead friend as he chased an impossible future.
So that the boy she loved could have the one measure of freedom she could give, Mikasa would do it all again.
Purgatorio, clad in the barest flicker of Touki that Mikasa's prodigious talent had garnered in weeks of training, carved through the back of the Attack Titan's skull.
Mikasa's fledgling Touki flickered out.
It had been enough.
Split horizontally, Mikasa's blades had carved through the base of the skull upwards and at an angle to line up with the jaw of the enormous creature.
Mikasa flew through the opening, ready to once more kill her heart.
To find it empty.
Her eyes widened, and Mikasa quickly flew through the hole she had created, fearing another surprise attack.
There was no attack.
With the base of its spine severed, the copy of the white, centipede-like Titan that had led this second Rumbling collapsed, its massive bulk surrendering under its own weight.
Mikasa watched it fall, eyes frantically searching the battlefield.
With Kuroka's confirmation that Eren could use the Warhammer at a distance, there had always been the risk that he would hide somewhere in the back just to let the Colossal Titans do their work from safety.
Mikasa had rejected that proposal entirely.
Eren would never do something like that.
It was too passive, too cowardly for him.
No, he'd be at the forefront, leading everything. Even if it were the riskier option, he could not help himself from being in the thick of things.
So where was he?
Mikasa had little time to search the battlefield for the slightest hint of the true Attack Titan.
As if the collapse of the fake Founding Titan was a signal, the dense cloud of smoke and dust started to thicken.
Removed from the battle for the moment, Mikasa was one of the few who noticed the mist closing in on the battlefront.
And, in the distance, the mist pooling at the bottom of Agreas.
The heat haze, the fog of war, and the struggle for survival had blinded everyone to oddity closing in around them.
Mikasa's heart fell.
She flew. Far from the front line. Far from the battle, which was one titanic distraction.
Because she couldn't trust anyone else to stop him.
Because Mikasa Ackerman was the only person in this world that Eren Yeager had once chosen over his dream, revenge, and life.
So Mikasa flew toward Eren, praying she'd make it in time.
She didn't make it.
With blood flowing from his nose and sweat slicking his body, Georg reminded the world why Dimension Lost was considered a high-end Longinus, even greater than Boosted Gear and Divine Dividing.
Mikasa Ackerman, the Underworld army, hundreds of High class and Ultimate class defenders, and thousands of Colossal Titans were all swallowed in a deep mist.
The Underworld lost its attackers to a pocket dimension that kept them trapped.
It lost its defenders to Eren Yeager.
CREATORS' THOUGHTS 
ReadingDangerously
ReadingDangerously One of my favourite aspects of fanfiction is the notion of a crossover. Two worlds/characters that were never meant to interact, colliding and creating something unique. And one of my favourite aspects of a good crossover is the handling of powers. When it's poorly written, it makes a story dull and boring. One side is stronger/better, and there is no contest, so the stakes grow dull. I hoped to do something better.
Titans, as a general rule in anime, are scrub-level. A team of well-trained humans can kill one with swords, and modern weaponry almost trivializes them. That was a recurring theme of season 4 of AOT. The power of Titans was on the way out, thus Eldia and Marley could no longer use them to dominate the world. The current human world could stop the Rumbling. It would undoubtedly have collateral damage, but most advanced nations would be able to drop a few high-powered bombs and stop Eren's apocalypse as soon as it started.
Sirzechs alone could solo the entire army of Wall Titans and Eren's white Founder form.
So, I found myself in the fun position of using the rules of both worlds, creating a conflict that was at once believable and engaging.
Enter Senjutsu and Touki.
Sairaorg has little talent but overcomes it with years of hard work and effort. Eren cheats. Mikasa? She was still better than Titan shifters who spent their entire lives training for war. She's older and more experienced than most devils or human sages. And she's an Ackerman.
I hope this little explanation shows how my mind works as I try to craft a story that is cohesive not only to characters but also to the rules of both worlds.
For example, Eren's shitty sensing doesn't matter to him because he uses the Paths to link him to his summoned Titans. Once they are summoned, he can see through their eyes. I took this method from how Ymir fought the scouts during the Battle of Heaven and Earth. Like then, even though there are no humans in the spines of the Titans Eren conjures, they are still destroyed if the nape is sliced. Eren can resummon them and doesn't need to keep them connected to his body like in his original world, but the rule is still the same. Senjutsu speeds up regeneration that is already present, and Touki makes things tougher, but the tactics Eren uses are all based on things he's either done or seen before.
I hope this little explanation shows how my mind works as I try to craft a story that is cohesive not only to characters but also to the rules of both worlds. The next few chapters are going to get... messy despite being some of my most anticipated, so I'd lay out a bit of my thought process for those interested.
I will meet you all on Friday on the bench.
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