Summary

Infinity Castle trilogy adapts high-stakes battles against upper moons with intense emotions and rivalry.

Zenitsu’s past with Kaigaku sets up an exciting battle showing intense character growth.

Zenitsu faces Upper Moon Six alone, highlighting his growth and the challenges ahead.

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Zenitsu, Kaigaku, and Their Ugly History

Jigoro Kuwajima’s Disciples Have Had a Rough Past

Demon Slayer: Infinity Castle trilogy is expected to be a visual treat as the films will adapt some of the most high-stakes battles in the series so far. As the Demon Slayer Corps prepare to confront Muzan and his underlings, humanity’s future rests on their shoulders. Unlike previous arcs, the battle will be fought on many fronts, with Upper Moons like Akaza, Kokushibo, and Doma playing a central role. But at the same time, a personal battle between two old rivals will ensue in the Infinity Castle, which has not received the hype that it deserves. What will separate this fight from any other battle in Muzan’s lair is its intensity, raw emotions, and personal rivalry that will put the adversaries to go above and beyond their physical limits.

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The following contains spoilers from Demon Slayer: Kimetsu no Yaiba manga and anime.
Zenitsu, Kaigaku, and Their Ugly History

Jigoro Kuwajima’s Disciples Have Had a Rough Past

A long time ago, Zenitsu was in debt of approximately 600,000 yen, adjusted for inflation. He had been duped by all seven of his ex-girlfriends, who never had any respect for him and treated him like a slave. Former Thunder Hashira Jigoro Kuwajima saw something in Agatsuma and rescued him from what he described as a mountain of debt. Zenitsu struggled immensely as his mentor started training him to become a swordsman. Despite Agatsuma’s several attempts to escape, he never gave up on him and ensured that his disciple kept working on himself.

Grandfather wasn’t senile. If I’m scum, then you’re trash. I feel sorry for grandpa for having such pathetic successors. I can only do the First Form and you can do everything except that!

While training under Jigoro Kuwajima, Zenitsu met Kaigaku, an extremely rude and violent individual. He not only looked down on Agatsuma but frequently bullied him. But because of his low self-esteem and cowardly nature, Zenitsu never stood up for himself. It could be assumed that he was probably bullied as long as he trained alongside Kaigaku since there is no evidence to suggest otherwise. Agatsuma eventually went on to become a demon slayer and didn’t see his bully for a while. Everything changed when Zenitsu received a mysterious letter while he was training with Stone Hashira Gyomei Himejima. It revealed that Kaigaku had accidentally crossed paths with Upper Moon One Kokushibo and had accepted his offer to join the Twelve Kizuki to save his life. When Jigoro learned about this, he was so ashamed that he committed seppuku. The horrifying details of his last moments enraged Agatsuma, and he transformed into a completely different person.
What Makes Zenitsu’s Battle With Kaigaku So Exciting?

Rivalry, Hatred, and an Ugly Past

In the Demon Slayer: Infinity Castle movie, fans are excited to see the Demon Slayer Corps fight against Kokushibo, Akaza, and Doma. But in all this hype, Zenitsu and Kaigaku’s battle perhaps went under the radar. Their ugly history sets up the intense battle ahead and causes them to take any means necessary to take each other down.

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It’s interesting that Kaigaku has just replaced Gyutaro and Daki as the Upper Moon Six. The brother-sister duo had occupied that position for over a hundred years and killed several Hashira during that time. Their combined combat experience made them a frightening combination that was not easy to put down. As a replacement, Kaigaku barely measures up to the duo. His inexperience makes him a somewhat easier target compared to any other Upper Moon in history. Demons tend to increase their power and maintain vitality by killing humans and eating their flesh. While it’s unclear if Kaigaku ate someone or not, it could be assumed that he could not have eaten enough flesh as other Upper Moons because he did not have that much time before an all-out war broke out. While these factors make Kaigaku significantly weaker than his peers, he is still a serious threat.

I hate myself more than anyone. I always think I have to get my act together, but I end up cowering, running away, sniveling. I want to change. I want to be a competent person. ~ Zenitsu Agatsuma

Meanwhile, Zenitsu has dramatically improved as a combatant since the battle in Swordsmith Village. The experience of fighting an Upper Moon has taught him many important lessons. Furthermore, the Hashira training helped him push past his physical limits and become stronger than ever before. Unlike any other previous battles, Agatsuma is no longer running away from the challenge ahead of him and is, in fact, eager to put his life on the line to avenge his mentor. This battle between an inexperienced Upper Moon and a demon slayer who is fast approaching Hashira level is going to be perhaps the most intense battle in the Demon Slayer: Infinity Castle trilogy. The fact that Agatsuma is all set to fight his arch-enemy alone makes it even more exciting.
Can Zenitsu Take Down an Upper Moon Alone?

Defeating an Upper Moon is always going to be a challenge, regardless of the circumstances. Even though Zenitsu played an important role in taking down the previous Upper Moon Six, he also had help from Inosuke, Tanjiro, Nezuko, and Uzui. This time, he will be all by himself and can’t expect others to come to his rescue.

If he wishes to win, Zenitsu will have to take advantage of Kaigaku’s inexperience and weaknesses. As difficult as it may be, Zenitsu does have a slim chance, but it is going to take a lot out of him.

Demon Slayer: Infinity Castle trilogy’s first installment is scheduled to be released in the United States on September 12, 2025.

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