Kaigaku is one of the most tragic and infuriating characters in Demon Slayer: Kimetsu no Yaiba.

And that's exactly why he's such a great villain.

A former student of Thunder Breathing and a fellow disciple under the same master who trained Zenitsu Agatsuma, Kaigaku possessed enormous talent and potential. By all accounts, he could have become a powerful Demon Slayer and a worthy successor to one of the most respected fighting styles in the Corps.

But Kaigaku wanted strength.

And more importantly...

He wanted it now.

What makes Kaigaku so compelling is that he serves as a dark reflection of Zenitsu. Both trained under the same mentor. Both struggled with feelings of inadequacy. Both wanted to survive in a dangerous world.

The difference was the choices they made.

Where Zenitsu learned to trust others and push through his fears, Kaigaku chose a path built on pride, resentment, and self-preservation. Faced with overwhelming danger, he accepted power from the demons rather than risk defeat, transforming himself into the very thing he once should have fought against.

Which is about as Demon Slayer as a tragedy gets.

Visually, Kaigaku looks incredible. His Thunder Breathing techniques already carried the dramatic flair associated with lightning users, but after becoming a demon, those techniques take on a darker, corrupted appearance. The result is a fighting style that feels familiar, yet deeply wrong.

Like seeing a hero's legacy twisted into something dangerous.

Fans love Kaigaku because he represents one of the series' strongest themes: talent alone is not enough. Skill matters. Potential matters. But character matters more. Kaigaku had many of the gifts needed to become a hero.

He simply lacked the wisdom to use them properly.

And that's what makes his story hit so hard.

Also... yeah... becoming the evil version of your former classmate is generally not considered a healthy career move.