Chapter 219: New Progress in Drug Development
Akira knew all too well that while the soft, lingering comforts of a peaceful life were intoxicating, he couldn't afford to become addicted to them. Not while Kibutsuji Muzan was still alive and lurking in the shadows.
If he let his guard down now, everything he cherished—his family, his home, the women he loved—would eventually burst and vanish like fragile bubbles.
Having slaughtered multiple Upper Ranks and spent an entire night aggressively greeting Muzan with a shout that echoed across the mountains, Akira was absolutely certain he had secured the Demon King's undivided attention.
While nothing could ever surpass Muzan's obsession with the Blue Spider Lily, Akira figured the ancient demon wouldn't mind taking a detour to eradicate a human who had thoroughly annoyed him.
Therefore, the path to victory was clear. He needed to eliminate Muzan's remaining subordinates as quickly as possible, find a suitable lure to draw the coward out of hiding, and seize the initiative to launch a decisive final battle while the Demon Slayer Corps was at its unmatched peak.
Aside from hunting down the remaining Upper Ranks, triggering that final clash required solving two massive problems: securing the lure, and finalizing the development of a specialized drug meant to weaken Muzan.
Akira already had a few solid leads regarding the former, but the progress on the latter remained a mystery.
Lost in his thoughts about their upcoming strategies, Akira strolled down the quiet corridors toward Tamayo's laboratory.
Roughly three months had passed since they successfully synthesized the drug to reverse demonization. Since then, Tamayo and Shinobu had practically lived in that lab, burying themselves in toxicological research. If it hadn't been for Akira's birthday—and his firm insistence that Shinobu honor her promise to balance work with rest—she likely wouldn't have stepped foot in the Butterfly Mansion yesterday.
"Lady Tamayo is conducting a critical experiment. Unauthorized personnel are strictly forbidden from entering!"
Akira paused, an eyebrow arching in genuine surprise. Standing squarely in front of the heavy wooden doors was Yushiro, acting as a fiercely loyal gatekeeper. Akira focused his gaze on the young demon. Yushiro's eyes were wide, trembling with a chaotic mix of absolute terror and stubborn defiance.
Since demons didn't sweat, Yushiro was spared the indignity of looking physically drenched, but his internal panic was painfully obvious. The arm he had thrust out to block Akira's path was shaking so violently it practically left afterimages in the air.
Ever since Akira had casually pressed a blade to his throat during their first encounter, it usually only took a single, flat look to send Yushiro scurrying away to preserve his own life. Yet here he was, terrified out of his mind, adamantly barring the way. It clearly proved that whatever was happening behind those doors was of monumental importance.
Amused by the display, Akira reached out. Yushiro squeezed his eyes shut, his face scrunching up as if bracing for decapitation. Instead, Akira just lightly patted his trembling shoulder.
"Your courage has grown quite a bit, hasn't it?" Akira said, his tone mild and conversational. "What exactly are they working on in there? I don't need to go inside, but telling me shouldn't be a breach of protocol, right?"
Truthfully, Akira appreciated this quirk in Yushiro's personality. He might be prickly and cowardly on a normal day, but when it truly mattered, he would stand his ground. Well, putting aside his incredibly twisted, obsessive devotion to Tamayo.
Yushiro cracked one eye open, swallowing hard. "I don't know the exact details of Lady Tamayo's research. I only know it involves a specialized compound targeting the Demon King. Lady Tamayo and that..."
Akira's eyes narrowed, a dangerous, silent pressure leaking into the air.
Yushiro choked on his words, forcibly swallowing the insult 'ugly woman' before it could leave his mouth. He cleared his throat nervously. "Lady Tamayo and... Miss Shinobu... specifically instructed me before they began. No one is allowed to disturb them until they emerge."
Akira nodded thoughtfully. Shinobu had mentioned last night, while curled up against his chest, that the drug development had entered its most critical phase. It was the reason she had practically sprinted back to the lab right after breakfast, leaving Akira to spend his morning sharing quiet, intimate moments with Kanae and Makomo.
It seemed they had finally reached the final stage.
Was it the aging drug? The cell-destruction drug? Or perhaps the development of multiple anti-Muzan poisons had all reached their climax at the same time?
Filled with a quiet sense of anticipation, Akira leaned against the wall outside the laboratory and waited.
He could easily use the Transparent World to peer through the thick doors and observe the room, but he wasn't a pharmacologist. Staring at bubbling vials wouldn't speed up the process. He just had to wait patiently.
The only reason he had the luxury to lounge around the estate right now was because someone else was currently shouldering his usual burdens.
After two months of intense recuperation, Kamado Tanjuro's frail body had made a miraculous, complete recovery. Following a brief period of physical adaptation, the older man's sheer combat prowess had exploded. In recent spars, Tanjuro had steadily suppressed Sabito—who was still struggling to fully grasp the Transparent World—and was now only slightly inferior to Akira himself in raw technique.
This was utterly absurd considering Tanjuro had never received formal, systematic training in any Breathing Style, nor did he possess actual battlefield experience against demons. If he had, the gap between him and Akira might be dangerously thin. To independently comprehend the Transparent World without a master, and to instinctively correct the fragmented, error-riddled forms of Sun Breathing passed down through his family... Tanjuro's innate talent was monstrous.
Recognizing this, Akira had happily waved a hand and dumped the exhausting task of staking out the Upper Rank Two, Douma, squarely onto Tanjuro's shoulders.
When informed of his new assignment, Tanjuro had offered a dry, exasperated smile. "I thank you so much."
"You're very welcome," Akira had replied without missing a beat.
Jokes aside, Tanjuro had already expressed a firm desire to join the Demon Slayer Corps. Whether it was driven by deep gratitude for saving his life, a father's wish to protect his family, or a righteous duty to eradicate demons, his resolve was absolute. With his mastery of the Transparent World and his current lack of official duties, he was the perfect man for the reconnaissance job.
Akira had even offered to fast-track Tanjuro to the rank of Hashira, given his overwhelming strength. But after careful consideration, Tanjuro had politely declined.
It wasn't a matter of dodging responsibility. Monitoring an Upper Rank was a suicide mission for most ordinary Hashira. Tanjuro simply didn't want to disrupt the internal stability of the Corps.
The privileges granted to a Hashira were massive. A Pillar held the absolute authority to command lower-ranked swordsmen, even ordering them into certain-death situations if the mission demanded it. Because of this heavy authority, a Hashira's position had to be built on a foundation of absolute, irrefutable merit. Without the blood of at least fifty demons or the severed head of a Twelve Kizuki on their record, the other swordsmen—many of whom had lost their entire families to demons—would never accept a newcomer being handed such power.
Understanding Tanjuro's wisdom, Akira hadn't pushed the issue. The Kamado family had no financial worries under the Corps' protection anyway.
So, the current dynamic was set: Tanjuro used his Transparent World to keep a constant, invisible watch over the Eternal Paradise Cult's headquarters during the day, while Akira used his terrifying speed to scour the surrounding territories at night, hunting for any trace of Douma's movements.
Since it was still daytime, Akira had a rare moment of peace.
He waited until the sun began to dip toward the western horizon, casting long orange shadows across the courtyard. Finally, the heavy laboratory doors clicked and swung open.
Tamayo and Shinobu stepped out. Despite the dark circles under their eyes, both women radiated a vibrant, electric energy.
"We succeeded!"
The moment Shinobu spotted Akira leaning against the wall, her exhaustion vanished. She launched herself forward, practically tackling him in a fiercely excited hug, cheering brightly. In the dizzying rush of their triumph, she completely forgot the solemn pact she had made with Kanae that very morning to ignore Akira for the entire day.
Not that Kanae had actually managed to follow that rule herself, anyway.
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