The "Water Lotus."
It was currently one of the most controversial, highly sought-after assassination spells circulating the Clock Tower. Rimuru had actually filed the patent for it himself.
He'd originally based it on a ridiculous weapon from a past-life wuxia novel, the Torrential Pear Blossom Needle. He designed it to be gorgeous, silent, and absolutely lethal. Naturally, the teenage magi of the Association thought it was the coolest thing ever.
The faculty had to frantically ban it from the curriculum after realizing the spell had a thirty-seven percent chance of violently maiming the caster.
But the ban only skyrocketed Professor Tempest's underground reputation as an avant-garde hydro-mancy artist.
Acht, however, wasn't a starry-eyed student.
The ancient homunculus terminal looked at the towering, liquid flower and saw it for what it truly was: a weapon of mass destruction draped in a pretty skin.
Too late to run.
Rimuru watched the homunculi frantically trying to retreat into the keep. He slowly shook his head.
The crimson lotus bloomed.
Tens of thousands of hyper-compressed, blood-laced water needles detonated outward in a spherical shockwave. It was a torrential hurricane of crimson wire.
The needles punched through the thick stone walls of the castle. They shredded the defensive bounded fields. They ripped through homunculi and Dead Apostles alike, painting every single inch of the winter courtyard a glossy, horrifying red.
Back at the tree line, the shockwave of the blast rippled through the freezing rain. Strout silently raised a hand, conjuring a canopy of black demonic fire that instantly vaporized the incoming bloody drizzle before it could touch Altrouge.
The Black Princess rested her chin in her hands. Her crimson eyes reflected the blooming carnage, glittering with profound fascination.
"His magecraft is truly beautiful, isn't it?" she murmured. "Especially when painted with blood."
"I fail to see the tactical value of aesthetics," Strout grunted, thoroughly unimpressed. "I am no grand caster, but even I know that level of flashy presentation is a senseless waste of mana."
"You don't understand." Altrouge let out a soft, chiming giggle. "What you consider 'unnecessary' is simply the standard a true artist holds himself to. The pursuit of perfection is never a flaw, Strout. And beauty can never be evil."
"That is…"
"His exact words to a student who questioned his methods." Altrouge lowered her gaze, a fond smile touching her lips. "It's the first time I've ever heard a magus preach such a philosophy. Fascinating, isn't it?"
…
The bloody rain finally tapered off.
Rimuru folded his spectral bat wings and touched down on the decimated, cratered earth.
It was a slaughterhouse. Mangled synthetic limbs and pulverized vampiric flesh littered the mud.
Beneath the splintered remains of the ancient pines, the few Dead Apostles strong enough to survive the horrific friendly fire were huddled together.
They stared at the masked Demon King who had just rained hell upon them, trembling in sheer terror, yet, in their feral eyes, there was a rabid, fanatical worship.
They crawled toward his boots like beaten dogs seeking their master.
At the shattered entrance of the castle, Acht was completely pale. His defensive barriers had barely activated in time to shield his core.
Seeing Rimuru land, the patriarch raised a trembling hand. His stoic, mechanical face finally cracked, contorting with rage and profound terror.
"What… what do you actually want?!"
Rimuru's little board-wipe hadn't just showcased firepower rivaling a Noble Phantasm. More importantly, it had instantly erased Acht's numbers advantage.
That was exactly why Rimuru had dropped a friendly-fire nuke without a second thought. His drafted vampire army was a mixed bag.
Sure, a few were decent fighters, but half of them were utterly useless trash that struggled against basic combat maids.
If Rimuru had let it play out as a war of attrition, the vampires would have eventually lost. Why? Because the Einzbern castle wasn't just a fortress; it was a factory.
Acht was a summoner who could infinitely churn out mass-produced homunculi to drown his enemies in bodies.
So, Rimuru bypassed the grind. He wiped out the trash mobs on both sides.
All the pawns die. Only the elites who can survive my AoE get to stay on the board.
High-tier combat homunculi required delicate magic circuits and meticulous tuning. Acht couldn't mass-produce them. He only woke them up in absolute emergencies.
But Rimuru had underestimated the psychological impact of his grand entrance. Dropping a boss-level nuke into a mob fight had completely shattered Acht's artificial morale.
As a humanoid terminal, Acht's raw combat power was pathetic; his expertise lay in Bounded Field construction, homunculus engineering, and Greater Grail theory.
He was a backline factory manager. He had zero chance against a Color-rank magus, let alone a proxy of the Twenty-Seven Ancestors.
Which was why Acht had essentially screamed, 'Take what you want and leave!'
He was surrendering. His core programming dictated one absolute priority: survive to realize the Third Magic.
But Rimuru hesitated.
Make a deal with this old bastard?
Rimuru thought of the canonical Fate/Zero timeline. Wasn't this the exact same stubborn, heartless relic who orchestrated Illyasviel's tragic fate? Honestly, Rimuru despised the Einzberns.
To solidify his new persona in the underworld, he needed the Church and the Association to take the Dead Apostle threat seriously. He needed them to crack down hard on the White Wing Lord's territory. To trigger that, he had to inflict catastrophic, undeniable damage here.
Furthermore, crippling the Einzberns now served a dual purpose: it would prevent them from dedicating resources to excavating Cornwall for the next few years, and it would guarantee they remained desperate enough to hire an outsider, Emiya Kiritsugu, when the Fourth Holy Grail War finally rolled around.
In short: as long as Acht didn't actually die, the harder Rimuru smashed this castle, the better the long-term payoff.
And besides...
Rimuru narrowed his eyes behind the Oni mask. Acht's smug little provocation from earlier was still rubbing him the wrong way.
You're literally just a programmed NPC. Who the hell gave you the right to talk trash to me?
….
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