In a daze, Kokushibou recalled an event that happened a long, long time ago.
It was about sixty years after he had become a demon, abandoned his name and human identity, and betrayed the Demon Slayer Corps.
He remembered it was a night like tonight, with the moon dyed red as if by blood.
At that time, he had witnessed something unbelievable while passing by a seven-story pagoda in the countryside.
He saw a person.
An old man, over eighty years old, with white hair and a face full of wrinkles.
He wore a kimono that felt extremely familiar to Kokushibou and carried a sword. Despite his aged appearance, Kokushibou recognized him immediately.
It was none other than his younger brother—Tsugikuni Yoriichi.
After about sixty years, he saw his younger brother again, the sun swordsman who had made him jealous, disgusted, and resentful for a lifetime.
At that time, he truly couldn't believe his eyes.
All those who bore the Demon Slayer Mark were supposed to die before the age of twenty-five.
As a result, Kokushibou had always thought that his younger brother, who had always overshadowed him, was long dead. Yet, not only was his younger brother alive, but he had also lived to be over eighty, which was simply unbelievable.
However, as he doubted his eyes, his younger brother, now an old man with white hair, shed tears.
"How sad... Brother..."
With tears in his eyes, his younger brother said those words and instantly took a stance—a flawless stance that exuded such strong pressure that Kokushibou almost couldn't breathe.
In the blink of an eye, his younger brother moved.
At that moment, he had no idea what had happened.
At that moment, he didn't even feel pain.
Even though his Transparent World was always active and he was much stronger than before after becoming a demon, he lost track of his younger brother and watched him disappear right before his eyes.
When he came to his senses, he realized that his younger brother had delivered the final slash of his life, landing behind him. Unbeknownst to him, he now sported a fresh cut on his neck, nearly beheading him on the spot.
At that moment, he had to admit that he truly trembled in fear.
What terrified him was that after sixty years, his younger brother, now an old man with white hair, could still deliver a strike with the same power and speed as in his prime, leaving him unable to react.
He understood that on that night, he almost died at the hands of his most hated younger brother.
However, his younger brother was exhausted after delivering that strike and died on the spot.
His younger brother's death allowed him to survive.
His younger brother's death also gave him a defeat that could never be recovered.
With his life as the price, his younger brother told him that even though he had become a demon and much stronger than before, he still couldn't block a single strike from his aged younger brother.
Humiliation.
Resentment.
Anger.
All these emotions surged in Kokushibou's heart that night, making him unable to forget the name 'Tsugikuni Yoriichi' for the rest of his life.
Because of this, he vowed never to lose to anyone other than Yoriichi in his lifetime and to assist Muzan in eliminating anyone who knew about Sun Breathing.
Now, as several hundred years had passed, he always thought he had forgotten that past and no longer felt humiliated by that unbearable memory.
Yet, he realized he had never truly let it go.
Clearly, the name 'Tsugikuni Yoriichi' had brought him too much jealousy, too much hatred, too much anger, and too many memories.
In such a situation, when Riezel appeared bearing the name 'Tsugikuni Yoriichi', Kokushibou lost all rationality and calmness, with only one thought left in his mind—to defeat him, to defeat the man named 'Tsugikuni Yoriichi'.
Whether it was to prove that he had surpassed his younger brother or for some other reason, perhaps not even he himself knew.
He only knew one thing—even after hundreds of years, he still had to live in his younger brother's shadow.
However, despite all that, he ultimately lost to 'Tsugikuni Yoriichi' once again.
Still with just one strike.
One strike, and he was defeated.
Defeated so miserably, so thoroughly.
"Are you satisfied?"
Riezel's voice slowly reached Kokushibou's ears.
"..."
Kokushibou was silent for a long, long time before finally, he spoke in a hoarse voice.
"Why... Just why can't I win against you..."
*Thud!*
With these words, Kokushibou's head slid off his neck and fell to the ground.
At the same time, his body was cut in half at the waist, one part falling to the ground while the other part slid against the moonlit wall, facing the desolate, lonely full moon and gradually losing its aura.
With the sun mural behind him still dazzling, Riezel calmly turned around, looking at Kokushibou, who was gradually turning to ashes.
"It was not Tsugikuni Yoriichi that you couldn't win against..." Riezel murmured slowly. "You just couldn't win against yourself..."
With these words, he turned around, intending to leave.
"Wait!"
Suddenly, a voice stopped him.
"..."
Riezel stopped, turned around, and as he looked at the voice's owner, his calm expression soon shifted to surprise.
"What are you two doing here?"
As he asked, he saw two figures appear out of thin air in a corner of the ruined, altar-like palace, approaching him.
He had seen this method of appearing once near the headquarters of the Demon Slayer Corps two months ago.
Yes, these two were none other than Tamayo and Yushirou.
"We infiltrated using the Blood Demon Art."
Tamayo answered Riezel's question, watching Kokushibou gradually turn to ashes and disappear, her expression complex.
"I didn't expect that even the Upper One wasn't a match for you... You're far stronger than I imagined..."
Tamayo naturally knew Kokushibou.
After all, she was a demon who had survived from the Sengoku period to the present, had seen Yoriichi, witnessed Muzan's pitiful condition, and, of course, had also encountered Michikatsu, Yoriichi's elder brother who had once betrayed the Demon Slayer Corps.
Because of this, she understood very well how powerful Kokushibou was.
In this world, the Upper Ranks were powerful beings, existing on a completely different level from other demons, including the Lower Ranks, who were regarded as ants by them.
Even the Hashira were helpless and no match for the Upper Ranks, as most of them who had bravely sacrificed themselves so far had died at the hands of the Upper Ranks.
Yet, even such Upper Ranks were nothing more than ants before Kokushibou.
Like how the Upper Ranks and the Lower Ranks were not on the same level, Kokushibou was also not on the same level as the other Upper Ranks.
Given this, Tamayo always thought that the only one capable of overpowering Kokushibou was Muzan, which meant that even if Riezel wanted to defeat Kokushibou, he wouldn't find it easy.
However, who would have thought that Riezel would surprise her so much?
He had proven with his strength that even the Upper One, second only to the Demon King, could not withstand his sword.
"Are you looking for the throne?" Tamayo asked solemnly. "I'll show you the way."
"Oh?" Riezel raised an eyebrow. "You know where this throne is?"
In response to his question, Tamayo replied with just one sentence.
"I haven't lived in vain for hundreds of years."
During these hundreds of years, besides researching drugs to counter Muzan and to turn demons back into humans, Tamayo had tirelessly investigated him, seeking every possible means to obtain information related to him.
Her Blood Demon Art involved injuring herself to generate illusions that could confuse anyone who smelled her blood, making it very useful for extracting and investigating information.
Yushirou, who had always followed her, possessed a Blood Demon Art related to vision, capable of obscuring others' sight or revealing things that were usually invisible, creating visual illusions that also greatly assisted her in her endeavors.
For this reason, Tamayo and Yushirou were able to infiltrate the Infinity Castle and map out its terrain.
"Follow me..."
Tamayo closed her eyes, murmuring as she suppressed certain emotions.
"Let everything end tonight."
She felt that perhaps this was her purpose for surviving until now.
Riezel looked at Tamayo silently and nodded a moment later.
And so, the three of them immediately left and headed toward the location where Muzan was.
===
At the same time, Kasugai Crows quickly spread the news of what had just happened at the altar-like palace.
"Head Instructor Tsugikuni Yoriichi has defeated the Upper One! Head Instructor Tsugikuni Yoriichi has defeated the Upper One!"
"Upper One! Defeated!"
"Casualties are zero!"
As this news reached the ears of every member of the Demon Slayer Corps, they were instantly filled with vigor.
"YOSHA—!"
"We defeated the Upper One!"
"Long live Lord Head Instructor!"
Every member of the Demon Slayer Corps erupted in cheers.
"Ho-How... How is this possible?!"
On the other hand, the demons, including the Upper Ranks currently in battle, couldn't believe their ears.
"Kokushibou... defeated?"
"So quickly...?"
"No! It can't be!"
"How could that Kokushibou be so easily beaten?!"
Not a single demon was without shock, nor dared to believe it.
Especially Kaigaku, who was currently fighting Tanjirou, Zenitsu, and Inosuke, was unwilling to accept this reality.
"How could he lose? How could he be beaten by a human?"
Kaigaku felt as if his faith had been shattered.
After all, the reason he became a demon was because of encountering Kokushibou, nearly being killed by him, and only surviving by begging for his life. He drank Muzan's blood out of a desire for immense power like Kokushibou's.
He knew very well how terrifying and powerful Kokushibou was, and yet, those crows said that Kokushibou had been defeated.
"Impossible!"
"Nothing is impossible!"
As Kaigaku yelled in disbelief, Zenitsu staggered to his feet and shouted at Kaigaku.
"Lord Head Instructor's strength is beyond anything you can imagine!"
"How does it feel?"
"The human you've looked down upon is now going to cut off your king's head!"
Zenitsu's shout sent an inexplicable panic through Kaigaku's heart.
'Are we... really going to lose?'