The battle between the Demon Slayers and Muzan had begun.
Muzan attacked first.
Countless tentacles erupted from his massive body, lashing out at high speed like a raging storm, tearing through the air from every direction. The space around them screamed under the pressure of the assault.
Erika moved instantly.
"Blood Breathing, Second Form — Crimson Rose Blooming Vortex."
Crimson ribbons unfurled from her arms, spinning outward in an omnidirectional vortex. The air filled with razor-sharp arcs of red as countless slashes bloomed in every direction, intercepting Muzan's tentacles one after another. The storm of flesh was halted, if only for a moment.
That opening was enough.
Demon Slayers and Type Null Units surged forward together, blades flashing. Nichirin swords struck Muzan's enormous body from all sides, cutting deep into the thick mass of flesh.
Only for the wounds to close almost instantly.
Shallow cuts vanished as new flesh swelled and knitted itself together, erasing every strike as if they had never landed. No matter how many attacks hit, none of them truly mattered.
Tanjiro gritted his teeth.
"It's not working, our attacks are too shallow!"
Obanai clicked his tongue.
"It can't be helped. This new form of Muzan is absurdly thick."
Shinobu frowned, eyes sharp behind her calm expression.
"My poisons aren't working well either."
Mitsuri hesitated, then asked, voice strained,
"Should we… cut off his neck?"
Obanai glanced at the grotesque shape in front of them.
"Sure, but where is the neck? That thing looks like a slug."
Akira watched the regeneration with narrowed eyes.
"He's in his ultimate form. Let's call him… Mega Muzan."
Even Akira's glowing purple blades carved only limited damage. The cuts didn't heal as fast as the others, but even then, fresh flesh crawled over the wounds, sealing them shut all the same.
Nothing they did was enough.
"Who cares what we call him?!" Erika snapped. "Tell me how to beat him, my attacks are doing nothing!"
Akira grimaced, eyes locked on Muzan's writhing mass.
"I'm still thinking. For now, just keep focusing on dealing with the tentacles."
As if responding to his words, Mega Muzan moved.
Despite his enormous body, he surged forward with shocking speed, barreling straight toward the nearby Demon Slayers. The floor creaked beneath his bulk as his shadow swallowed them whole.
"Ah…shiiit!" Akira cursed.
He dismissed his swords mid-run. They wouldn't do enough here.
Instead, he stepped in front of the charge and drove his fist forward.
"Falcon Punch."
A massive flaming falcon erupted from his punch, screeching as it slammed into Muzan's body. The impact stopped Mega Muzan dead in his tracks, flames roaring outward as the force rippled through his grotesque form.
That instant was enough.
The Hashira and Type Null Units rushed in together, striking as one, pouring everything they had into pushing Muzan back. Mega Muzan staggered, only briefly, before his flesh convulsed again.
Then came the next attack.
New tentacles burst from his body, far thicker than before. Each one was as massive as Zohakuten's wooden dragons, twisted flesh-drakes with gaping mouths at their ends. They lunged forward at terrifying speed, tearing through the air toward the Demon Slayers.
The Demon Slayers and Type Null Units moved to intercept.
"What the hell are those?!" Inosuke shouted, hacking wildly. "They look creepy as hell!"
Zenitsu said with unusual seriousness. "They're fast…! There are way too many of them!"
Erika lashed out with her ribbons, forcing several back, but more pushed through.
"They're strong too! I can't block them completely!"
Akira summoned his swords again and charged in, slashing through the incoming mass.
"He's stronger now… I guess this is stage two."
Selena's voice echoed in his mind, utterly unimpressed.
"I don't know, bro. This feels more like stage four or something."
Shinobu frowned sharply.
"How do we beat them? As a poison user, I'm not very useful here."
Akira exhaled hard.
"Right now? The best idea is to just fight harder, I guess."
As if mocking them, even more massive tentacles erupted from Muzan's body. Enormous mouths split open along them, and shockwave energy blasts fired downward in relentless barrages, raining destruction across the battlefield.
Everyone scattered, dodging desperately, but the attacks kept coming.
They were being overwhelmed.
Akira turned sharply toward the Type Null Units.
"Guys. Go."
The Yoriichi-Type Null Units didn't hesitate.
They all nodded at once.
Every single one of them entered Overdrive simultaneously.
Energy erupted from their bodies, pressure surging outward as all six swords each unit wielded ignited in glowing red light. In the next instant, they launched themselves toward Mega Muzan.
Their blades moved like a storm.
Six swords per unit shredded through Muzan's massive tentacles at blinding speed. Flesh was torn apart again and again, some units even carving directly into the main body itself, forcing Muzan to roar in fury.
Still, they didn't stop.
Watching them, Erika's expression tightened.
"Is it really okay to make all of them go Overdrive at the same time?"
She knew the risk. After Overdrive, Type Null Units will enter a cooldown period, a complete shutdown. And if they all did it together, they'd all fall at once.
Akira didn't look away from the fight.
"It couldn't be helped. Those tentacles are too dangerous, and the Demon Slayers are getting exhausted."
He clenched his fist.
"Using all their Overdrive at once creates massive damage. That's a good thing right now."
And he was right.
The Type Null Units tore massive chunks from Mega Muzan's body, their glowing red blades disrupting his regeneration. For the first time, his healing slowed, just slightly, and for a moment it looked like he was taking actual damage.
But it was enough to matter.
Soon, Muzan was forced back, cornered.
But then he began his next attack.
All across his grotesque body, multiple mouths split open, stretching wider and wider as energy gathered within them, the air vibrating ominously.
"Everyone…! It's the shockwave attack!" Tanjiro shouted.
The battlefield froze for a split second.
Everyone tensed. They all knew what that attack meant. With this many mouths opening at once, the power would be far beyond anything Muzan had unleashed before.
Akira felt his own body stiffen.
He didn't know how to block something like this.
With the number of mouths and their sheer size, this would be an attack larger than anything they had faced so far. He knew he and the Type Null Units would survive, but everyone else… he wasn't sure.
Worse, the Type Null Units were on the verge of entering cooldown.
And Erika couldn't possibly create a ribbon shield large enough to protect everyone at once.
As Akira searched desperately for a solution, something clicked.
"Wait…This is the Infinity Castle. It has floors.And they're made of wood."
Akira moved instantly.
He leapt high into the air, not toward Muzan, but toward the floor beside him, and unleashed a powerful Flaming Kick straight downward.
"Falcon Kick."
The already-strained floor shattered.
Mega Muzan's massive body plunged through the broken surface before he could release his attack, crashing into the floor below.
But his momentum and his overwhelming weight didn't stop there.
He smashed through another floor.
And another.
And another.
Akira kicked off the air itself, flipping back upward, and landed hard on the remaining platform.
"Take cover!" he shouted.
The words had barely left his mouth.
When Muzan's shockwave attack detonated.
The explosion was colossal.
Even though Muzan was now several floors below, the blast ripped upward through the castle, tearing through layers of wood and stone. The shockwave slammed into their floor, hurling everyone violently as blinding white light swallowed everything.
When Erika opened her eyes, the first thing she saw was Akira's face.
She realized she was lying on top of him.
His Eclipse armor was gone, unsummoned, his body braced beneath hers.
"Are you fine?" Akira asked.
"I am," Erika said, quickly pushing herself up.
She looked around and froze.
They weren't on the same floor anymore.
"Where are we?" she asked.
"A few floors below," Akira replied. "When I saw you falling, I jumped down too. The others should be on the floors above us."
Erika nodded and stood fully.
Then she heard it.
A sound from below.
She peered down through the shattered hole in the floor.
On the level beneath them, Muzan was still there.
His body was heavily damaged, torn, and broken from the Type Null Units' Overdrive attacks.
And yet.
He was still healing.
Slowly.
But unmistakably.
"He's still alive," Erika said, staring down through the broken floor. "He's healing back. What should we do now?"
Akira rose to his feet beside her, his gaze fixed on the grotesque shape below.
"…I don't know," he admitted. "By now, all the Type Null Units should have entered cooldown. And I'm not sure about the condition of the others either. That explosion was too big."
"Then what are we supposed to do?" Erika pressed.
Akira exhaled slowly. "Maybe… just leave Muzan alone. Let the poison finish him off."
Erika turned sharply toward him. "Didn't you say yourself that it's better not to leave things to chance? That it's better to finish him off with our own hands?"
"I did," Akira replied. "But right now, he's just too hard to kill. As I said before, I'm sure all the Type Null Units are in cooldown, and after that blast, I don't know how many Demon Slayers are still in fighting condition."
"But we have to do something," Erika said firmly. "There has to be a way."
Just then, Selena's voice echoed in their minds.
"There is actually an easy way to defeat Muzan now."
Akira stiffened. "Easy…? What is it?"
She continued. "The easiest way to defeat him, and any creature of darkness for our family, is to use Stellar Radiance."
Akira fell silent.
"…Can I even use that?" he asked quietly. "I've never managed to activate it before."
Erika remembered.
Stellar Radiance, the Starlight Family's special power, a devastatingly effective power against creatures of darkness. It was the same power Akira had once used to defeat the giant werewolf when they were children.
But she also knew Akira couldn't activate it.
It required powerful emotions, love, hope, and bonds.
And Akira… wasn't someone who could normally feel emotions that intensely.
Even back then, he hadn't activated it on his own. He had only managed it because Selena had lent him her power.
Akira knew that too.
"I can't just activate it like the others," he said. "I never could."
"Brother," Selena said gently, "I have a feeling you can use it now. Just concentrate on your feelings for Erika-chan."
Akira hesitated.
"What if I can't? What if it didn't work?" he thought.
Selena's voice softened. "Are you worried that your feelings for Erika-chan aren't real? That they're just an illusion you created yourself?"
Erika looked at him in shock.
Akira didn't answer.
He couldn't.
What if his feelings weren't real?
What if he reached for them… and there was nothing there?
He wanted them to be real.
But what if they weren't?
What would he do then?
Selena giggled lightly. "The fact that you're afraid right now means you can feel them. Don't worry, brother. Believe in yourself. You can do it."
Then she added, "Erika-chan, say something too."
Erika let out a quiet sigh and looked straight at Akira.
"Akira," she said, "just do it. It's not like you to hesitate this much."
"But what if my feelings aren't real?" Akira asked. "What happens then?"
Erika didn't look away.
"I believe in the bond we have," she said calmly. "In the time we spent together. No matter what happens, my feelings won't change."
She met his eyes without hesitation.
"I believe in us."
Akira stared at her serious expression.
And finally realized.
It was time to stop running away.
"…Alright."
Akira closed his eyes.
He let everything else fade away and reached inward, toward the memories that surfaced the moment he thought of her.
How they first met.
The time they spent together as children, playing, arguing, laughing.
How Erika would always scold him, yet never leave his side, no matter how many stupid things he did.
The quiet moments they shared. Their outings.
How she stayed with him, chose to be his friend, when in his previous life, children his age had only feared him.
He remembered the pain of being separated from her.
The emptiness that followed.
And then the happiness he felt when they reunited, how she stayed with him again, walking beside him through this dangerous world without hesitation.
The more he remembered, the more he felt something stirring inside his chest.
He didn't know if it was love.
But if it wasn't love… then he didn't know what else it could possibly be.
So he reached for it.
At first, nothing happened.
Then, faintly, something answered.
A soft, ethereal glow bloomed around his body.
A fragile, star-speckled purple aurora shimmered into existence, delicate but undeniable, like distant starlight breaking through heavy clouds.
Akira slowly opened his eyes.
He stared down at his hand, watching the faint radiance flicker across his skin.
"…I did it," he said quietly.
That meant his feelings were real.
Even if the light was faint, it was there.
Selena's voice rang with warmth. "Yeah. I knew you could do it, brother."
Erika looked relieved, genuinely happy. She let out a breath she hadn't realized she was holding.
But Akira frowned slightly. "It's faint, though. It's not as strong as when Mother used it… or when I borrowed it from you." He hesitated. "Can I really beat Muzan with this?"
As he spoke, Erika felt something stir deep within her chest.
A pull.
A certainty.
She didn't know what it was, but she knew she had to act.
Before Akira could react, she stepped forward and wrapped her arms around him, hugging him tightly.
She closed her eyes, focusing.
Akira stiffened at the sudden contact. "Erika…?"
She didn't answer.
For a moment, Akira wondered if she had hugged him simply because she was happy, because he had real feelings for her.
But Erika was doing something else.
Just as she had when Akira turned into a werewolf, she synchronized her heartbeat with the Sacred Gear inside him, Lunar Vows.
She didn't know why she did it.
She only knew that she had to.
Their heartbeats aligned.
And then.
Boom.
Stellar Radiance erupted from Akira's body.
Not faint.
Not fragile.
A massive surge, on the same scale as when his mother had used it, burst outward, flooding the space with overwhelming starlight.
Akira gasped, shock washing over his face. "What…? These feelings… they're overwhelming." He swallowed. "They're not mine."
Selena answered calmly. "They're Erika-chan's. She synchronized your hearts using the Sacred Gear and boosted you with her own feelings she felt for you."
Akira stared, stunned. "It can… do that?"
"Yes," Selena replied. "We can talk about it later. For now, go finish Muzan."
Akira nodded slowly.
He looked down at Erika, who was still holding onto him, and felt it again, that overwhelming sensation. It was similar to what he had felt when he activated Stellar Radiance himself, yet several times stronger. Far stronger than anything he had ever experienced.
If those feelings belonged to her about him…
Then was this what it meant to love someone?
And more importantly, could he ever return those feelings to her in the same measure?
The question lingered, heavy and unresolved.
But there was no time for it now.
He realized that before anything else, he had to finish the fight.
Gently, he separated himself from her embrace and looked at her directly.
"I will be back," he said.
Erika smiled without hesitation. "I know."
Akira turned.
His gaze locked onto Muzan below, and a confident smirk curved his lips.
"It's over, Muzan. I finally have the power of love now," he declared casually. "I don't think I can lose to anyone anymore. You're so finished."
Watching him joke around, both Erika and Selena let out tired sighs.
Yeah. Akira had definitely returned to normal.
Stellar Radiance surged around him, responding to his will. The light condensed, reshaping itself into two radiant katana formed entirely of starlight.
Without another word, Akira leapt down to the floor below, landing directly in front of Muzan.
Muzan snarled and attacked instantly. His tentacles lashed out in a frenzy, rushing toward Akira from all directions.
But Akira didn't tense.
He looked… relaxed.
Happy, even.
He moved.
Using the only form of the breathing technique he had created himself.
"Star Breathing, First Form— Flashing Comet."
A blinding purple streak tore through the Infinity Castle.
Akira moved like a falling star, his blade flashing once.
With that single slash, Muzan's flesh turned to ash at the point of contact.
Akira didn't stop.
He knew this was the moment; his technique had to evolve.
So he continued moving, his path carving light directly into reality itself. His motion traced a perfect five-pointed star, each line burning bright as Muzan's massive body disintegrated into ash along the way.
Then Akira came to a halt.
"Pentagram."
The glowing five-pointed star completed itself in the air.
Then the light collapsed inward.
And Kibutsuji Muzan, the demon who had terrorized the world for a thousand years, vanished.
Dissolved entirely into pure Stellar Radiance.
Just like that.
The nightmare that plagued this world has ended.