Teru meticulously packed his luggage, readying himself for the journey ahead.

In the Taishou Period, people didn't burden themselves with excessive belongings when they traveled.

"I'm heading out now," Teru announced.

Muzan seemed absorbed in her books, paying little attention to his words.

"Have a pleasant journey? Alright, blessings received!" Teru nodded, half talking to himself. He went out and closed the door.

The tea table remained silent, undisturbed like the calm water in the teacup.

"Have a pleasant journey." Muzan responded.

"What did you say?" The door was suddenly opened and Teru inquired.

Muzan sat quietly, seemingly immersed in the tranquil act of sipping tea, as if her earlier words had vanished like a fleeting illusion. With a wave of his hands, Teru smiled and left.

Shortly after, Muzan put down her medical book and spoke to an empty space, calling out a name, "Kokushibou."

Without a trace of the door opening or closing, not even the rustling of the wind, a man dressed in Warring States attire appeared before her, kneeling respectfully.

He had flame-like marks on his neck, wearing a purple snakeskin kimono.

This was Kokushibou, the first of the Upper Ranks, a formidable and taciturn warrior. In Japanese, the name ‘Kokushibou’ symbolizes darkness and death.

Over hundreds of years, he had served Muzan faithfully, exterminating countless Hashiras, and even before becoming a demon, he had been one of the most powerful humans. His strength was beyond question.

Muzan pondered for a moment before finally issuing her command.

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"Go protect Teru."

Kokushibou's calm eyes betrayed a hint of surprise, for this was the first time Muzan-sama had ordered him to protect a human. Nevertheless, he composed himself and nodded, accepting the task as part of the grand plan to annihilate the Demon Slayer Corps.

"Yes." The samurai replied, leaving the room as silently as he had arrived.

Meanwhile, Teru leisurely strolled through the streets, heading towards the train station. The gentle rain showered upon him, its subtle touch suggesting a possible break in the clouds, yet the rain persisted. Teru relished such weather; it reminded him of the days he could take leisurely walks with his wife, unbound by the constraints of sunlight. Since marrying Muzan, he had developed a fondness for such overcast days, but deep down, he still cherished the sunny days.

With a resolve in his heart, he encouraged himself, determined to work hard at the medical conference in pursuit of a cure that would allow his wife to see the sun.

With these thoughts in mind, he arrived at the train station.

"Mugen Train Ticket, destination: Spider Mountain."

He said as he handed over his ticket to the conductor. Soon, he found the designated train which rested quietly on the tracks as they extended into the distant fields.

It was a sight that filled him with admiration for the charm of Taishou Era.

As he boarded the train, a commotion nearby drew his attention.

"Sir, do you have a train ticket?" Asked the conductor.

"Ticket? What's that?" Replied the poker-face man with confusion.

"And why are you carrying a sword, sir? It's not allowed to have weapons on the train."

"For killing."

The policemen exchanged puzzled glances and hesitated whether to arrest him or not. Yet before they could take any action, Giyu Tomioka, the Water Hashira, disappeared between carriages.

Hmm, interesting! If it were an ordinary day, Teru would have struck up a conversation, but he had pressing matters to attend to.

The train began its journey, and on the roof, Kokushibou stood, gazing pensively at the town receding into the distance.

Without a single omen, a sword came slashing towards him, meeting him face to face!

Kokushibou deftly parried the attack, forced back by the immense power.

After a fierce exchange of blows, they intuitively ceased their assault, taking a few steps back in unison.

The man before him wore a demonic mask and a peculiarly designed white Haori.

"Who are you?" His voice seemed altered.

Kokushibou hadn't been injured for hundreds of years, yet now he looked surprisingly at the cuts in his arms. He couldn't help but marveled at the skills of his opponent.

The samurai fixed his gaze intently upon his adversary, a growing excitement welling within him.

However, the mysterious swordsman vanished from sight.

Kokushibou, intrigued yet focused on his mission, turned his attention to Teru, whom he was assigned to protect.

He observed Teru leaning against his seat, looking a bit unwell.

Can't be him. Was it a Hashira from the Demon Slayer Corps?

With a shake of his head, Kokushibou returned to his post on the train's roof, his eyes closed in silent vigilance.