Could Kokushibo Defeat Muzan If He Were A Demon Slayer?

Pavas Gagneja
Apr 5
3 min read

Updated: Apr 12

Kokushibo, the Upper Moon 1 Demon from Demon Slayer, and Muzan Kibutsuji, the original Demon and series’ big bad, are two of the most terrifying characters in the series. But here’s a wild what if: Could Kokushibo, with all his power, actually beat Muzan, if he switched sides and became a Demon Slayer?

First, some context. Kokushibo is Muzan’s strongest follower - a 500-year-old Demon with Moon Breathing techniques, insane regeneration, and a grudge against his human past. Muzan, meanwhile, is the source of all Demons, a near-invincible monster who fears only the sun. Their relationship is like a god and his favorite weapon, but what if that weapon turned against him?

UPDATE: This article was updated by Daksh Chaudhary on April 8th, 2025. We have added a YouTube Short based on this article for a better explanation of how the battle between Kokushibo as a Demon Slayer and Muzan would look like.

Watch our YouTube video to see if Kokushibo, as a Demon Slayer, could defeat Muzan Kibutsuji.

ALSO READ: Demon Slayer’s Success Is Hurting The Anime Industry (And Here’s Why)

Kokushibo’s Power: What Makes Upper Moon 1 So OP?

Even as a Demon, Kokushibo is built different. His Moon Breathing forms are so advanced that they make other Demons look like toddlers with sticks. He can create crescent-shaped blades from his flesh, regenerate instantly, and sense enemies through his six eyes. Plus, he’s got centuries of combat experience: he was a swordsman rivaling Yoriichi, the guy who almost killed Muzan.

If Kokushibo became a Demon Slayer, he’d lose his Demon regeneration and sunlight weakness (since he’s no longer a Demon). But he’d keep his swordsmanship, gain a Nichirin blade, maybe black or blood-red, given his vibe, and potentially unlock a Demon Slayer Mark. Imagine Moon Breathing + Marked power: now that’s a recipe for chaos.

Muzan’s Weaknesses: The Demon King's Flaws

Muzan’s strength is absurd; he can morph his body into whips, claws, and mouths, absorb Demons, and heal faster than Kokushibo. But he’s not perfect. His biggest weaknesses are:

The Sun: Instant death.
Tamayo’s Drug: Slows his regeneration.
His Ego: He panics when cornered.

ALSO READ: Why Kaigaku Betrayed The Demon Slayer Corps And How It Changed Zenitsu

If Kokushibo became a Slayer, he’d know all these weaknesses. He’s seen Muzan’s powers up close for centuries. Plus, as a human, he could exploit Muzan’s fear of the sun by stalling until dawn; something Demons can’t do.

The Fight: Moon Breathing Vs Body Horror

Kokushibo vs Muzan Kibutsuji Demon Slayer

Let’s picture this battle. Kokushibo, now a Demon Slayer with a Mark, faces Muzan in a dark city. Muzan starts with his usual arrogance, attacking with flesh-tentacles and shockwaves. But Kokushibo counters with Moon Breathing’s wide-range slashes, cutting through Muzan’s limbs.

Muzan would regenerate, but Kokushibo’s knowledge of his patterns gives him an edge. He’d target Muzan’s seven hearts and five brains, just like the Hashira did. Without Demon regeneration, Kokushibo would need to avoid fatal hits, but his skill and speed might save him, considering he kept up with Marked Muichiro, Genya, and Gyomei, all at once.

The wild card? The Demon Slayer Mark. If Kokushibo unlocks it, his strength and speed could spike to Yoriichi-like levels. And if he gets a Bright Red Nichirin blade (which slows Demon healing), Muzan’s in trouble.

Final Verdict: Kokushibo Could Defeat Muzan, But In Certain Conditions

Could Kokushibo win? Yes, but only if the fight happens near sunrise and he has a Mark + Bright Red blade. Kokushibo has the skill, knowledge, and Breathing Techniques to damage Muzan. But Muzan’s raw power and regeneration are insane - without the sun or Tamayo’s drug, even Kokushibo would get worn down.

The real kicker? Kokushibo’s mindset. As a human, he’d fight with purpose, not just hunger. His pride as Yoriichi’s brother and his hatred for Muzan’s control could push him beyond his limits. But Muzan’s desperation to survive makes him equally dangerous. So, can Kokushibo defeat Muzan? Yes, but only with perfect timing and every advantage. And honestly? We’d pay to see it.