In the memories Izuna had received from his clone, Kokushibo had flown into a frenzy midway through their fight.
He had attacked wildly while complaining about how Izuna could possess such immense power when they were both Swordsmen of the Demon Slayer Corps.
Then Izuna's clone had said something that sent him completely over the edge.
"If you're useless, take a good look at yourself instead of whining about it here."
After hearing Izuna's account, Tetsuya clicked his tongue.
"Tsk, that really hit him where it hurt."
If Tetsuya remembered correctly, Michikatsu Tsugikuni, otherwise known as Kokushibo, had a deep obsession with power.
It stemmed from the fact that, despite being the eldest son of the Tsugikuni family, his talent fell short of that of the second son, Yoriichi Tsugikuni. That had always eaten at him.
No matter how hard he worked, he remained overshadowed by Yoriichi Tsugikuni's brilliance.
In the end, Michikatsu Tsugikuni had become a demon to gain greater power and surpass his younger brother.
Izuna's words had undoubtedly struck him right where it hurt most.
"Oh, Tetsuya, I noticed something else in the memories I received from my clone."
"What else did you find?"
"That Demon King has been searching for something that will let him overcome sunlight. Also, when he ambushed me, he mentioned something called Sun Breathing."
"Something to overcome sunlight, and Sun Breathing?"
Tetsuya found that strange. He knew Muzan was searching for the Blue Spider Lily to overcome sunlight, but why would he bring up Sun Breathing?
What Izuna used was Flame Breathing, which he had copied from Kyojuro Rengoku.
"Izuna, why did that Demon King mention Sun Breathing to you?"
Izuna frowned as he answered.
"I came back a little too late. My clone had been gone for a while, so a