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

Daksh Chaudhary
Mar 29
3 min read

Updated: Apr 12

Why Kaigaku betrayed the Demon Slayer Corps explained

If you’ve ever wondered why Kaigaku betrayed the Demon Slayer Corps, the answer isn’t as simple as “he was evil.” It was a result of hunger for power, which ultimately turned a promising warrior into one of the series’ most tragic villains. But his betrayal didn’t just destroy his own life. It also lit a fire under Zenitsu Agatsuma, the once-cowardly boy who became a hero.

Kaigaku and Zenitsu started as polar opposites. Both were students of Jigoro Kuwajima, the retired Thunder Hashira, but while Zenitsu whined and cried through training, Kaigaku acted like he was already a legend. While Kaigaku wanted glory, Zenitsu just wanted to survive. But when Kaigaku betrayed the Corps and became a Demon, everything changed. This is the story of how one man’s weakness became another’s strength.

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Fear Over Honor: Why Kaigaku Betrayed The Demon Slayer Corps

Reason why Kaigaku betrayed the Demon Slayer Corps

Kaigaku wasn’t born a traitor. He was a talented swordsman with a fatal flaw: he cared more about looking strong than being strong. When his master, Jigoro, took in Zenitsu, a crying mess who could barely swing a sword, Kaigaku felt insulted. He saw Zenitsu as a waste of time, someone unworthy of their master’s attention. But deep down, he was scared. Scared of failure. Scared of dying. And that fear ate away at him.

Everything came crashing down during a Demon attack. Kaigaku was given a mission to protect innocent lives, but when faced with a powerful Demon, he froze. Instead of fighting, he abandoned his comrades and ran. To survive, he made a deal with the devil - literally. He let Muzan, the king of Demons, turn him into a monster. In that moment, Kaigaku chose cowardice over courage. He traded his humanity for power, thinking it would make him invincible. But it only made him a slave.

Zenitsu’s Turning Point: From Crybaby To Thunder Warrior

Zenitsu’s journey was the opposite of Kaigaku’s. At first, he hated being a Demon Slayer. He screamed at the sight of danger and begged others to save him. But Kaigaku’s betrayal hit him like a lightning bolt. When Zenitsu learned that Jigoro, the man who saved his life, had killed himself out of shame for Kaigaku’s actions, something snapped. He couldn’t run anymore. He had to make things right.

This was Zenitsu’s awakening. He stopped relying on luck or hiding behind others. Instead, he focused on the one thing he was good at: the First Form of Thunder Breathing. While Kaigaku had mocked him for only knowing one move, Zenitsu practiced it until he could move faster than the eye could see. He even created his own technique, the Seventh Form: Honoikazuchi no Kami, a blazing strike that combined speed and precision.

The Final Showdown: Thunder Vs Thunder

When Zenitsu finally faced Kaigaku in the Infinity Castle, it was a clash of ideals. Kaigaku, now Upper Moon Six, fought with arrogance, using six different Thunder Breathing forms. But his attacks were messy and fueled by anger. Zenitsu, meanwhile, stayed calm. He didn’t waste energy on flashy moves. He waited, focused, and struck with a single golden lightning slash.

Kaigaku’s Demon powers couldn’t save him. Zenitsu’s strike was too fast, too precise. As Kaigaku crumbled into ash, he finally understood his mistake. He’d spent his life chasing power, but Zenitsu had found something stronger: purpose. In his final moments, Kaigaku realized his mistake, but it was too late for him. However, his failure taught Zenitsu a priceless lesson: true strength comes from protecting others, not yourself.

Final Verdict: Two Paths, One Lesson

Kaigaku’s story is a warning. He had talent, but he let fear and pride control him. The answer to why Kaigaku betrayed the Demon Slayer Corps lies in his desperation. He thought becoming a Demon would make him unstoppable, but it turned him into a puppet. His betrayal ruined his master’s legacy and hurt everyone who trusted him. But his actions also sparked a hero. Without Kaigaku’s betrayal, Zenitsu might’ve stayed a scared kid forever.

Zenitsu’s victory wasn’t just about avenging Jigoro. It was about proving that courage isn’t the absence of fear, it’s fighting despite fear. Kaigaku ran from his weaknesses; Zenitsu faced them. Today, fans remember Zenitsu as the Thunder Breathing prodigy who mastered himself before mastering his sword. Kaigaku? He’s a cautionary tale of wasted potential.