Akaza's death put Muzan, who had only just begun to relax, on edge again.
"Damn it. First there was that Mirror Hashira who mastered multiple Breathing Styles. Who has appeared this time? Someone actually managed to kill Akaza."
Muzan knew Akaza's strength all too well.
Ever since Akaza became a demon, he had killed countless swordsmen from the Demon Slayer Corps, including quite a few of their so-called Hashira.
Yet now, someone had actually killed Akaza.
Could it have been the Stone Hashira, reputed to be the strongest? Or perhaps that mysterious Illusion Hashira?
Whatever the case, he absolutely could not sit around waiting to die. He immediately ordered the demons under his command to find out who had killed Akaza.
For a time, the demons, who had been keeping a much lower profile, became active again.
Even the Upper Ranks out in the field received Muzan's orders to take part in the investigation.
But none of that activity outside could disturb Tanjiro, who was still recuperating at the Butterfly Mansion.
With nothing else to do, Tetsuya picked up his Nichirin Blade and went looking for those demons.
He intended to use them to test the Breathing Style he had developed by combining the Hinokami Kagura dance Tanjiro had demonstrated with other concentration-based Breathing Styles.
The demons active throughout Japan were dumbfounded. Why was this Illusion Hashira everywhere?
Sometimes he appeared in Osaka, sometimes in Tokyo. At times, he was in Hokkaido one moment and appeared in Kyushu the next.
There was simply no predicting him. It terrified the demons, who feared that the elusive Illusion Hashira might appear right before them at any moment and cut off their heads.
Unlike Tetsuya, Izuna did not travel around everywhere, though he, too, had gleaned a great deal from the Hinokami Kagura.