This article contains spoilers from the Demon Slayer manga.

Demon Slayer is the biggest anime of the season with the release of the first Infinity Castle movie. Akaza Returns is slowly taking over the world, with Japanese fans being the first to witness the opening chapter in the final battle between the demon slayers and Muzan’s army of demons. It can be argued that no anime comes close to Demon Slayer at the moment, as it continues to shatter box office records.

Part of the film’s success can be credited to the explosive fights set in the Infinity Castle. With ufotable’s animation, fans are guaranteed fluid fighting scenes, clever camera angles, and impressive combat choreography. However, one fight, in particular, feels completely out of place in Demon Slayer’s Infinity Castle arc. Even manga fans who finished reading the series will probably agree it nearly ruined the arc.

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By Rei Penber

Zenitsu and Kaigaku’s Fight Nearly Ruined the Infinity Castle Arc

An Out-of-Nowhere Fight in Infinity Castle

Zenitsu and Kaigaku's fight came out of nowhere in the Infinity Castle arc.
The Zenitsu vs. Kaigaku fight had no real build-up, unlike the other fights.

Who would have thought that Zenitsu Agatsuma would get a solo match despite his track record in Demon Slayer’s Infinity Castle arc? Out of the main trio, Zenitsu was probably the last character fans expected to see fighting alone in the most dangerous place in the series. After all, for most of Demon Slayer’s story, he was always afraid of facing demons, in fear of losing his life.

Then there’s Kaigaku, Jigoro Kuwajima’s former student and Zenitsu’s senior. Fans have only seen glimpses of him in Demon Slayer, unable to track down his drastic character development. He started as an orphan, then he abandoned his humanity just to keep on living, as revealed in other characters' stories. Even his demonification was done behind the scenes, with fans only hearing the news in Zenitsu’s letter.

With this technique... I wanted to fight you as an equal.—Zenitsu to Kaigaku

Then, all of a sudden, Zenitsu and Kaigaku found each other in the Infinity Castle to settle their conflict. Their fight came out of nowhere, with manga fans feeling like they missed an entire arc when they faced each other in the castle. In other words, there’s no actual buildup to Zenitsu and Kaigaku’s fight, in comparison to the other fights set in the arc. Its awkward timing and lack of depth nearly ruined the momentum of the arc, despite it being Zenitsu’s redemption moment.

Kaigaku Is an Underwhelming Demon in Infinity Castle

Kaigaku Is Only a Filler Upper Moon

Among the upper moons, Kaigaku might be the only demon who received little exposure in both the anime and manga. That’s mostly due to the timing of his demonification and Muzan’s need for new upper moons to replace the dead ones. In fact, it hasn’t been a year since Kaigaku abandoned his humanity by accepting Kokushibo’s offer to become a demon working under Muzan.

Because of this, Kaigaku obviously lacks the skills and knowledge to use his blood demon art to its maximum potential. While the author gave him a chance to redeem himself with his new powers, the downside was that he had no idea how to use them to his advantage. This allowed Zenitsu to finish Kaigaku, which, in turn, made Kaigaku’s character feel hollow and flat.

If I'm scum, then you're trash.—Zenitsu to Kaigaku

Unlike other demons with emotional complexity and rich backgrounds, Kaigaku only appears in the Infinity Castle just to talk down to Zenitsu, insult his former teacher, and get killed the easiest and the fastest. It’s almost as if he was inserted in Infinity Castle just to give Zenitsu the cool moment that all Demon Slayer fans have been waiting to see from day one.

Zenitsu and Kaigaku’s Story Needs More Development

Zenitsu and Kaigaku Need Their Own Mini Arcs

For most Demon Slayer fans, Zenitsu and Kaigaku’s story could have had more emotional weight if the author had spent more time developing their characters. Understandably, fans lost Zenitsu for an entire arc, and the same goes for Inosuke, while Tanjiro fights to the death in the Swordsmith Village arc. If only they had seen them running into serious trouble while they were away, fans would have been more understanding.

On the other hand, Kaigaku had little screentime in the series, with fans only seeing him from flashbacks. Due to the pacing of Demon Slayer, he did not receive any spotlight until he was in Infinity Castle fighting against Zenitsu. Because of this, most fans believe Zenitsu and Kaigaku deserve mini arcs to flesh out their characters more. The conclusion to their rivalry could have been better with more buildup and depth instead of forcing them into a short fight in the Infinity Castle arc.

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