What Is an Astronomy Major Worth? A Sudden Twist!

Within Infinity Castle, every demon was under Muzan Kibutsuji's control.

Thus, he learned at once of Kokushibo's death, as well as the sight he had witnessed in his final moments—

The figure of a swordsman as dazzling as the blazing sun.

"No!"

"There's nothing to fear!"

Muzan Kibutsuji slammed his palm against the armrest and rose abruptly.

His face was livid as he paced the hall restlessly, frantically weighing the pros and cons in his mind.

"The Blue Spider Lily is within reach. This may be the only chance I'll ever have!"

"There's no need to fear him! He is no monster like Yoriichi Tsugikuni!"

"The Upper Ranks will soon wipe out those insects from the Demon Slayer Corps!"

"Then I'll have Nakime summon every demon here. How can a mere human stand against me!"

"Then let's see the strength of this 'mere human' you keep talking about."

Thunder Form: Light Fang!

Daylight burst forth, accompanied by thunderous force!

Kashu moved like a flash of lightning, severing Muzan Kibutsuji's neck in a single strike!

As his head regenerated, Kashu turned his left hand into a blade and thrust it into Muzan's chest and abdomen. He crushed the vial, then swiftly leaped back.

The newly regenerated Muzan Kibutsuji immediately sensed something wrong inside his body, and a savage grin spread across his lips.

"Foolish beyond belief! You actually think you can poison me?"

He confidently began breaking down the poison invading his body, only to discover in horror that it had already spread through him like maggots clinging to bone. It was spreading so quickly that he had no time to react!

"This is!?"

Kashu's lips curled slightly as he explained with a smile.

"You remember Tamayo, don't you? This is the carefully prepared 'surprise gift package' she and I made especially for you."

"Once you're poisoned by this, forget about splitting into chunks of flesh and running away."

Muzan Kibutsuji tried it in disbelief. Sure enough, his ability to split apart had truly been tightly restrained!

Tricked time and again by inferior creatures he regarded as insects, the already brutal and bloodthirsty Demon King became even more frenzied.

He suddenly raised his head, his crimson eyes glaring viciously at Kashu.

"You disgust me to the point of nausea! Do you think these petty tricks can defeat me?"

"A natural disaster, an earthquake—either can easily take countless lives. Do you hate the heavens? Do you hate the earth?"

"Just treat me as a natural disaster!"

"Why do you always wave the banner of revenge, going on and on about your parents and loved ones being killed, endlessly coming to bother me!!!"

Kashu calmly watched the completely unhinged Muzan Kibutsuji, idly rolling an intricately constructed metal sphere between his fingers. His eyes were filled with undisguised contempt.

Before long, the distinctive rasping cries of Kasugai Crows rang out beside Kashu's ears.

It meant that the members of the Demon Slayer Corps had begun to notice his encounter with Muzan Kibutsuji.

At the same time, it signaled that the time had come.

"A natural disaster? You think you're worthy?"

The smile on Kashu's face deepened as he casually tossed out the metal sphere in his hand.

Amid a series of crisp, precise clicks as its mechanisms meshed together, a radiance truly comparable to the blazing sun suddenly bloomed!

It was the nemesis of demons—the light of the sun that purged all filth and evil!

As the artificial sun's rays poured over Muzan Kibutsuji, his skin immediately began to sizzle and emit blue smoke.

The searing pain made him let out a shrill scream, and he turned to flee.

Lightning flashed again!

Kashu rammed into him with overwhelming force, then drove his platinum longsword forward in a furious thrust, pinning Muzan Kibutsuji firmly to the wall!

"Let go of me! Let go of me now!"

"I don't want the Blue Spider Lily anymore! I don't want it! Please, let go of me!!!"

With his entire face embedded deep in the wall, Muzan Kibutsuji's voice now carried an almost pleading sob as his screams continued without end.

When the shadow of death truly enveloped him, ultimate life-form, immortality, eternal life—he cast all of it from his mind!

Yet at that very moment, shrill screams no less agonized than his own began echoing wildly through his mind.

Those were the desperate death cries of the demons under his command as sunlight shone upon them.

The situation had completely surpassed Muzan Kibutsuji's comprehension. His severely inadequate brain simply could not process this scene that overturned everything he knew.

Keeping the sword hilt pressed against his opponent, Kashu saw from Muzan Kibutsuji's terrified, bewildered expression that the plan was proceeding smoothly. He lowered his head and chuckled softly.

A demon's vitality truly was terrifyingly tenacious. Even when cut in half or dismembered, they could rapidly regenerate. But—

When he learned that demons would turn to ash the moment they were exposed to sunlight, Kashu had nearly laughed his head off.

Not to mention that scientists of this era were already attempting to simulate sunlight.

As someone from an astronomy major, he needed only a few ordinary materials to create a more convenient and efficient "artificial sun."

Afterward, to determine whether only genuine sunlight worked against demons, or whether light with the same properties would suffice, Kashu specifically conducted two experiments with Tamayo.

The first was a simple blood-sample exposure test.

The second was a random unlucky demon captured during the day.

If Muzan Kibutsuji had made a habit of reviewing his subordinates' memories.

If Muzan Kibutsuji had been even a little more cautious in his daily life.

If Muzan Kibutsuji...

Unfortunately, there were no ifs in this world.

That demon which died beneath the daylight had not aroused the slightest suspicion from Muzan Kibutsuji—

After all, there were occasionally idiots who accidentally got themselves killed by the sun.

Muzan Kibutsuji's arrogance, ingrained to the marrow of his bones, was undoubtedly his most fatal weakness.

Yet it was precisely because of this that Kashu had managed to secure a trump card capable of deciding the battle.

"A fatal mistake made in the early stages of war can never be remedied."

"Checkmate, Muzan."

Kashu shifted his body slightly, allowing the "sunlight" released by the metal sphere to "coat" every inch of Muzan Kibutsuji's skin more evenly.

"AAAHHH!!!"

The once supremely arrogant progenitor of demons rapidly decayed and dispersed, clumps of ash-gray embers drifting down in soft flurries.

In the end, only Kashu remained, along with a floor full of dust.

Kashu swept his gaze over the ashes on the ground and let out a long breath. Then he lowered his head to look at Fou, who lay obediently curled against his collar.

"Though luring him in was a bit troublesome, the mission was finally completed perfectly."

"It's been over two months since my abilities were updated. I suddenly really want to see Loki's reaction."

"Fou!"

!!!

The pure white beast and Kashu's own instincts simultaneously sounded a piercing warning!

The relaxed Kashu reacted without the slightest hesitation, abruptly shooting backward into the distance!

Boom—!

A thorny whip made of flesh and blood tore through the air with a thunderous crack.

Wrapped around it was a strange suction force, and it viciously shattered the ground where he had been standing moments earlier!

Kashu lowered the arm he had used to block the flying debris, his sharp gaze fixed on the figure before him—

The resurrected—or rather, reappeared—"Muzan Kibutsuji."

This guy was absolutely not the Muzan Kibutsuji from before!

Although he possessed the exact same appearance, even with Transparent World activated, Kashu could not sense his existence at all!

I can't sense him. I can only observe him with my eyes?

The artificial sun is still operating. It seems this guy inherited Muzan Kibutsuji's abilities, but not his weakness of fearing sunlight?

I really hope whoever issued this mission explains things more clearly next time. I nearly capsized in a ditch.

Kashu still had many unanswered questions, but that did not affect his ability to make the correct judgment.

Without a doubt, this "Muzan Kibutsuji" before him was the true target of his mission!

Clang—!

The platinum longsword reappeared amid the swirling motes of light.

For the first time since leaving the dungeon, an eager smile appeared on Kashu's face.

"I hope you can take a beating better than that useless Muzan Kibutsuji!"