When Nezuko saw Raiden crouch down, her eyes lit up. She rushed forward and jumped into his arms, rubbing her head against his chin like a spoiled pet.
"Nezuko?"
Feeling her warmth, Raiden grew more confused.
Nezuko had not fully returned to being human, but she had always been sensible. Even without speech, she understood situations well and never interrupted when something serious was happening.
So why now?
After nuzzling his chin, Nezuko smiled with quiet satisfaction. Then she lifted her small hand and tapped the sheath of Raiden's Nichirin blade.
"Mmm, mmm."
To avoid accidentally hurting her, Raiden had already sheathed his sword. Defeating Muzan was only a matter of time, so he had no reason to rush.
Seeing her gesture, he hesitated for a moment before carefully drawing the blade and placing it into her hands. His movements were slow and deliberate, making sure she would not get hurt.
Nezuko held the blade with both hands.
A pink flame suddenly ignited from her body, spreading along her arms and onto the Nichirin blade.
The blade's temperature rose instantly. Its reddish gold color deepened, shifting into a vivid blood red.
Raiden's eyes sharpened.
A Crimson Blade.
This kind of blade could drastically slow a demon's regeneration. At its peak, it could prevent recovery entirely.
The wound left on Muzan by Yoriichi Tsugikuni had never healed, even after centuries. That alone proved its effectiveness.
Raiden might still fall slightly short of Yoriichi, but the difference was no longer significant.
With a Crimson Blade in hand, Muzan would not get another chance to recover.
"Mmm, mmm."
Nezuko pressed her hands against Raiden's knee and nodded firmly, as if urging him forward.
Raiden smiled faintly.
Good timing.
He fully drew the blade. Heat radiated from it, distorting the air around him.
Although this Crimson Blade was created through Nezuko's Blood Demon Art, Raiden quickly grasped the principle behind it.
Temperature.
Total Concentration Breathing increased blood flow and heart rate, raising body temperature and pushing physical ability to its limit.
When that heat reached a certain point, the Demon Slayer Mark would manifest.
If that same heat was transferred into a Nichirin blade, it would awaken a Crimson Blade.
This conclusion came naturally to him after observing Nezuko's flames. The finer details could wait.
Raiden patted Nezuko's head and stood.
"Snap."
With another crisp sound, an even denser cluster of flesh appeared.
Raiden raised an eyebrow.
In the short moment he had been distracted, Muzan had split into even more fragments. Some had already reached the outer edges of the Infinity Castle, nearly escaping.
"Sizzle."
Raiden swung his blade.
A crimson flash cut through the air.
This strike was completely different from before. The moment the blade touched the flesh, a sharp burning sound echoed.
The smell followed instantly.
Thick, charred stench filled the air as the fragments burned.
Flames spread along the blade, devouring each piece.
The flesh that had been regenerating suddenly stopped.
Raiden watched closely.
Black smoke rose from the fragments as charred marks spread rapidly across them. Under the intense heat, they lost all vitality.
No regeneration.
Raiden's expression sharpened with satisfaction.
This was the end.
Muzan clearly sensed it too. The remaining fragments began fleeing faster, scattering in all directions without any clear path, as if trying to escape Raiden himself rather than the castle.
Raiden's lips curved slightly.
It was rare to see Muzan like this.
"Sizzle, sizzle."
With each swing of his blade, more fragments were erased.
Then, with another snap, the final piece was pulled into view.
The fragment froze for a split second during the spatial shift, then began struggling violently the moment it sensed Raiden.
It expanded rapidly.
Flesh twisted and swelled, forming a grotesque giant infant.
Its body was smeared with blood, its eyes filled with fear and malice.
The infant opened its massive mouth, black smoke pouring out as it let out a harsh roar.
It lunged toward Raiden, massive hands reaching to devour him.
Those hands were swollen with veins, nothing like a child's.
Raiden remained still.
There was no fear in his eyes, only calm focus, with a trace of curiosity.
A sharp metallic sound rang out.
A flash of blade light cut across the space.
The giant infant froze mid-motion.
Everything went still.
Its eyes widened in terror and unwillingness, but it could no longer move.
A dull thud followed.
Its head slid from its neck and hit the ground.
The body began to collapse, decaying into black smoke that quickly faded into nothing.
Only the head remained for a moment, staring at Raiden with deep hatred.
If things had happened differently, if Raiden had been dealt with earlier, none of this would have occurred.
No.
It was not his failure.
It was Akaza.
It was Kokushibo.
It was Nakime.
All of them had failed him.
If Kokushibo had killed Raiden, if Nakime had found the Ubuyashiki estate sooner, everything would have been different.
Useless. All of them.
But no matter how strong his resentment burned, Muzan's life was already slipping away.
At the very end, his gaze remained fixed on Raiden, as if trying to carve his image into memory.
"Raiden…"
The faint whisper faded.
And with it, Muzan disappeared from the world.