Demon Slayer: This Upper Moon Is More Pathetic Than Terrifying, and He’s in the Infinity Castle

This article contains spoilers from the Demon Slayer manga and Infinity Castle Movie.

The initial installment of the “Demon Slayer: Infinity Castle” trilogy has just been released in Japan, leaving the rest of the world eagerly anticipating the grand finale on the big screen. Sales have been setting new records, and it’s expected to grow even more popular once it hits international cinemas. The future looks bright for “Demon Slayer: Infinity Castle” movie, suggesting that its success is all but guaranteed.

As an eager fan, I’m thrilled to share that the title of the first film in the Infinity Castle saga, “Demon Slayer: Infinity Castle—Part 1: Akaza Returns,” hints at its extensive content based on the manga. The most striking clue is the return of Akaza himself, suggesting this movie will likely introduce a new upper moon demon who may be more pitiful than fearsome.

Demon Slayer: Infinity Castle Part 1 Will Introduce Upper Moon Kaigaku

Kaigaku Is the New Upper Moon Six

Kaigaku replaced Daki and Gyutaro as Upper Moon Six.
The new Upper Moon Six, Kaigaku, has a shared history with Zenitsu.

Typically, when an upper moon, a powerful demon in our ranks, falls, another takes its place to maintain order. Just as Daki and Gyutaro, the demon siblings from the Entertainment District story, were replaced by a new demon after their demise, becoming the Upper Moon Six. This newcomer was none other than Kaigaku, who once wielded a slayer’s blade but was transformed into a demon when Upper Moon One, Kokushibo, bestowed upon him Muzan Kibutsuji’s blood during the Infinity Castle arc events.

In the initial film of the Demon Slayer: Infinity Castle series, Kaigaku prepares to showcase his enhanced thunder-style abilities infused with his demonic essence, in full view of his junior, Zenitsu Agatsuma. It’s important to note that both Kaigaku and Zenitsu were students under the ex-Thunder Hashira, Jigoro Kuwajima, many years ago. While Zenitsu is limited to using only the first form of thunder breathing, Kaigaku can utilize all forms apart from the initial one.

In the upcoming Infinity Castle film, it is foreseen that Kaigaku and Zenitsu will clash, not as partners in unity, but as adversaries with opposing ideologies. Given the movie trailer, spectators are eager to witness their fierce battle play out on the cinema screen. It’s common knowledge among fans that there can only be one authentic wielder of thunder-breathing techniques, and the winner will inherently claim the title.

Demon Slayer: Infinity Castle Part 1 Will Humiliate Kaigaku Like Never Before

Kaigaku’s Pathetic Fate in the Demon Slayer Manga

Kaigaku believes it’s alright to be shameful just to continue living.
Kaigaku brags louder than his thunder claps in Infinity Castle.

Before Kaigaku transformed into a demon, he had spent his human years in misery. Abandoned and alone, he managed to survive by stealing, scavenging for food scraps, and drinking from puddles. It was Gyomei Himejima who offered him refuge. However, instead of reciprocating Gyomei’s kindness, Kaigaku tricked a demon into Gyomei’s temple, intending to prolong his own life. This demon ended up slaughtering the other orphans, but Kaigaku himself survived the carnage.

After that, Jigoro Kuwajima accepted Kaigaku and started teaching him thunder breathing alongside Zenitsu. Yet, Kaigaku harbored a high opinion of himself, finding it distasteful to share the position of Thunder Hashira with someone like Zenitsu, who lacked dignity or courage. The situation became even more difficult as other demon slayers whispered about Kaigaku, suggesting he would never become the Thunder Hashira due to his inability to master its fundamental techniques, no matter how diligent he was in his training.

Until you die, you haven’t lost.—Kaigaku

In my viewpoint, the pitiful existence of Kaigaku didn’t cease at that point. Once a demon slayer, now pleading for mercy before an insurmountable adversary like Kokushibo, Kaigaku found himself in such a predicament. Rather than exerting all his might to defeat Kokushibo, he drained every last drop of Muzan’s blood within him – clinging to life as his only hope. In the depths of his despair, he harbored a fervent dream that, so long as he lived, the fruits of his disgrace would one day be his.

It appears that the Infinity Castle isn’t an ideal setting for Kaigaku to boast about his recent powers and expound on his philosophies. Despite gaining significant strength by consuming humans, he was unsure how to effectively employ his newly acquired skills. If the battle had taken place a year later, Kaigaku would have been an indomitable force with the power to breathe thunder.

Zenitsu’s Blade Sealed Kaigaku’s Pathetic Fate

There Can Only Be One True Thunder Breathing Successor

When fans of “Demon Slayer” witnessed Zenitsu opening his eyes within the Infinity Castle, they understood that he was dead serious about the situation. Following the contents of the letter during the Hashira Training arc, Zenitsu realized it was time to confront Kaigaku to resolve their issues permanently. He had to conquer his fear and apprehension, as avoiding conflict with Kaigaku was no longer an option. He knew he wouldn’t be able to meet his master peacefully in the afterlife if he let fear control him instead.

In simple terms, I couldn’t care less about people who don’t appreciate me. On the other hand, I am constantly dedicated to serving those who recognize and value what I bring to the table.

For the very first time in the Infinity Castle storyline, Zenitsu awoke with his eyes open. The moment of truth had arrived, as the scene for his battle against Kaigaku was meticulously prepared. There’s only one rightful heir to the Thunder Breathing technique, and Zenitsu was determined to prevent someone like Kaigaku from seizing the title, thereby preserving his master’s honor and reputation.

Fans of Manga understand that though Kaigaku’s slicing blows can pierce Zenitsu’s skin and char his flesh, the valiant demon slayer responds with a fresh version of Thunder Breathing. In this critical instant, Kaigaku will lose his head, and his desire to witness Zenitsu perish will vanish along with him. This way, Kaigaku meets his end solitarily, unfulfilled, and filled with bitterness until the very last moment.

2025-07-20 20:08