The Kingdom of Farmus, fueled by relentless propaganda from the Western Holy Church and the manipulative influence of hidden agents (likely tied to Yuuki Kagurazaka), officially declared a "Holy Crusade" against the Jura Tempest Federation.
They viewed the monster nation as a threat to human supremacy and a potential source of great plunder.
The invasion force was massive: a professional human army backed by zealous knights and, most dangerously, a small, highly effective group of Otherworlders (summoned heroes with unique skills) provided by the Church's network.
Arthur and Rimuru, receiving intelligence on the scale of the approaching army, gathered their commanders.
The Federation's military forces—led by Benimaru and supported by the Oni and High Orcs—were formidable, but they were still outnumbered by the sheer mass of the human army.
Arthur's counsel was grim and focused on minimizing loss of life.
"We cannot afford a long war of attrition. We must choose a perfect defensive chokepoint and use our superior skills and technology to shatter their morale instantly."
Rimuru, hardened by Arthur's training, agreed.
"We will not allow them to reach the city. We will defend our borders with everything we have."
The Federation forces established a strong defensive line at a narrow pass far from the capital, leveraging Kaijin's engineering and Geld II's construction skills to fortify the position.
The battle began with immense ferocity. Benimaru and the Oni fought with devastating effectiveness, using fire magic and overwhelming skill against the professional human soldiers.
However, the human army's numbers were vast, and the Otherworlders provided by the Church were specifically tasked with bypassing the main line and causing chaos.
A small contingent of these powerful human mages, utilizing specialized teleportation magic and powerful Holy barriers, successfully breached the outer defenses and targeted the capital—the undefended heart of the nation.
The ensuing scene was chaos. The human soldiers, driven by fanaticism and granted access by the mages, stormed the residential areas.
They targeted the most vulnerable: the unarmed civilians, including the children of the Goblin and High Orc families, as well as several of the children Rimuru had saved (who were protected by Shuna's emergency shields, but were forced to witness the massacre).
The immediate casualties were heartbreaking.
Many of Rimuru's beloved Goblin citizens, their families, and several High Orcs were killed before the main forces could double back.
The sight of innocent blood spilled in the city she vowed to protect shattered Rimuru's foundational pacifism.
Arthur, who had remained at the command center with Rimuru, felt the wave of death wash over the city.
His knowledge of the story was not useful anymore.
He could not predict everything. He could not prevent everything from happening.
Butterfly effect… It was hard to control. It was impossible with just his power alone.
His eyes, usually controlled, flared with a primal, cold rage—the fury of a True Dragon whose protective vow had been violated.
He immediately unleashed a targeted, non-lethal Dragonic Aura pulse that instantly paralyzed the human invaders in the city, halting the massacre.
The invading force was frozen, unable to move or think, awaiting their fate.
He turned to Rimuru, but she was silent. Her mind was a torrent of agony, sorrow, and terrifying resolve.
The Great Sage had locked down, processing the single condition for Demon Lord evolution: The need for ten thousand human souls.
Rimuru rose, her figure radiating a power far colder and darker than any monster had ever seen. She looked at Arthur, a silent, devastated appeal in her eyes.
"Arthur,"
She transmitted, her voice empty.
"They killed my children. They must pay the price, or this nation is meaningless. I must save them."
Arthur understood the magnitude of the choice.
He knew that the only way to revive the dead and protect their future was to complete evolution.
He made the final, necessary sacrifice of his strategic position.
"I will secure the souls,"
Arthur promised, his voice low and absolute.
"But you must complete the evolution, Rimuru. You must become the True Demon Lord you were meant to be."
Arthur moved with terrifying speed. He placed Rimuru in a secure, shielded location, leaving the terrified, paralyzed human invaders to her will.
He then rejoined the front line, not to fight, but to end the war instantly and secure the necessary souls for the ritual.
He unleashed a fraction of his Ultimate Skill: Magicule Breeder Reactor, coupled with his Reality Blending.
He didn't harm the allied forces; he executed a precise, localized magical strike on the entire human army on the front lines, killing the entire force of 20,000+ invaders instantly, cleanly, and without bloodshed—harvesting their souls for Rimuru's evolution.
He immediately returned to the capital and placed the sealed souls before the shattered, silent Rimuru.
Rimuru, witnessing the swift, terrifying execution by her Dragon Guardian, embraced the darkness.
She absorbed the souls, and the process of evolution began.
The magical pressure that followed was world-shattering, establishing her as the newly ascended True Demon Lord—a power now capable of rivaling even Arthur in certain aspects of raw magicule flow.
The city was silent. The dead were revived by Rimuru's new power, and the Kingdom of Farmus was destroyed, its army annihilated by Arthur.
The Jura Tempest Federation survived, but it was forged in tragedy and protected by an absolute, terrifying declaration of power.
Rimuru was no longer a naive Slime; she was a sovereign willing to sacrifice all for her people, guided and protected by her True Dragon Guardian.
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