The following contains spoilers from the Demon Slayer: Kimetsu no Yaiba manga and anime.
Summary
Quick Links
Demon Slayer: Kimetsu no Yaibais a story of suffering, self-discovery, retribution, revenge, and love. At its core, it focuses on a battle between good and evil with the future of humanity at stake. Since the conflict is extremely violent, over the years, personal rivalries have emerged that drive the demon slayers to push themselves even more, sometimes to the point that they perish in the process.
However, as one could infer, not all such feuds are comparable in intensity. Those driven by deep personal loss and tragedies carry far more weight and have become a critical aspect of the show’s overall narrative. Perhapsthe most vitriolic one is between Kaigakuand Zenitsu, whose shared past has now put them up against one another in a battle of survival in the Infinity Castle.
Zenitsu and Kaigaku’s Rivalry
The Bully and the Underdog
Zenitsu and Kaigaku are no strangersto one another. Many years before the two found themselves up against each other, they used to be the disciples of the former Thunder Hashira Jigoro Kuwajima. The experienced demon slayer had taken them under their wing and was helping them join the Demon Slayer Corps and become better individuals. But it appears that Kaigaku never truly valued his lessons and bullied Zenitsu for being timid. He looked down on Agatsuma and frequently mocked him for being untalented.
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.
At some point, Zenitsu ended uppassing the Final Selectionand became a demon slayer. He lost touch with Kaigaku, who was never a friend to begin with. Agatsuma later met and befriended Tanjiro, Nezuko, and Inosuke. The group has embarked on many missions since then and has become an inseparable team. While Zenitsu was busy turning his life around, Kaigaku also became a demon slayer. It appears that the two never crossed paths with each other, and at some point, Kaigaku had the misfortune of running into Kokushibo.
In order to save his life, Kaigaku accepted the offer to become a demon and was eventually picked by Muzan toreplace Gyutaro and Dakias the new Upper Moon Six. When Jigoro learned about this, he could not tolerate the embarrassment and took his own life. His last moments were filled with agony and suffering. Until this point, Zenitsu had remained a timid and cowardly person who detested training or fighting demons. But when he learned about the death of his master and realized who was responsible for it, Agatsuma’s fear of death disappeared, and he turned into a ruthless warrior determined to exact revenge.
Infinity Castle Movie Will Reveal Who is Stronger
Zenitsu Faces an Uphill Battle in Infinity Castle
In the Infinity Castle arc, Kaigaku is all set to face his arch-enemy, Zenitsu. Even the trailer confirms this by revealing the moment the two finally cross paths with each other after many years. It is evident from Zenitsu’s expression that he is determined to put everything on the line to avenge Jigoro Kuwajima. Meanwhile, Kaigaku also sounded self-assured, perhaps because he most likely received Muzan’s blood after joining the Twelve Kizuku.
Until this point, Agatsuma needed to enter an unconscious state to fight demons, but it appears that overcoming the fear of death has allowed him to conquer his mind, too. It will be an exciting battle since the duo knows so much about each other. They havelearned the Thunder Breathingunder the same master and also have some idea of each other’s shortcomings. Agatsuma can only use one form of Thunder Breathing, which is a serious weakness that an Upper Moon can easily take advantage of.
However, Zenitsu has shown in the past that he can be quite innovative, as he himself invented various extensions of Thunderclap and Flash technique named Sixfold, Eightfold, and Godspeed. If he wishes to survive an intense battle against someone like Kaigaku, he must create moves that he hasn’t used in the past, as the ones he has already created have proved to be not effective enough tokill an Upper Moon.
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!
On the other hand, Kaigaku’s transformation into a demon makes him extremely unpredictable for Zenitsu. The good thing is he appears to be still relying on his old fighting style, as he was carrying a sword when the twomet each other in the Infinity Castle. However, it would be a mistake to underestimate him, despite his lack of experience as a demon.
Kaigaku most likely has several sinister tricks up his sleeve that Zenitsu is yet to learn about. Their rivalry, coupled with an emotionally charged desire to defeat one another, makes their battle an intense showdown that will go down as one of the best battles in the series.
Demon Slayer: Infinity Castle trilogy’s first installment is scheduled to be released in the United States onSeptember 12, 2025.
