The Demon Slayer Movie: Mugen Train which was released in October 2020 saw one of the legendary Hashiras being killed in a fight against one of the upper fives. Kyojuro Rengoku, the Flame Hashira, was involved in an intense battle against Akaza, the Upper Moon 3 of demon leader Muzan’s demonic horde. Though Rengoku gave his all during his fierce encounter with Akaza, he was not able to eliminate the demon. Rengoku died from his severe battle injuries leaving the younger demon slayers, Tanjiro and Inosuke in tears and grief.

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It Was a Tremendous Means to Introduce an Upper Moon Demon

During the introductory season of the anime show, we got to see the strength and abilities of various Lower Moon demons. We also realized that the Hashiras were a great force to be reckoned with after watching some intense actions of Hashiras, such as Giyu Tomioka, Shinobu Kocho, and Kyojuro Rengoku.

Still, we didn’t really know the implication of the Upper Moon demon category. Of course, the demons had to be way stronger than Rui the formidable Lower Moon 5 or the show would’ve been considered sloppy. So, the creators of the show didn’t mind killing off a powerful Hashira to prove that battling the Upper Moon demons isn’t just a stroll in the park. Poor Rengoku!

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His Death Was Needed to Motivate Tanjiro, Inosuke, And Zenitsu To Train Harder

Before Rengoku’s painful demise, the younger demon slayers were training at a relatively sluggish pace. While Tanjiro was inspired to kill Muzan as a revenge against killing his mother and siblings, Inosuke and Zenitsu had less tangible reasons to train as demon slayers.

However, as Tanjiro and Inosuke witnessed Rengoku’s heroic death, they realized they had to put in more effort to become better demon slayers. Zenitsu also learns that he can’t climb to the position of a Hashira by being weak and lazy. Thus, Rengoku’s death was significant.

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It Paved Way For Tanjiro To Become The Fire Hashira

Though Tanjiro primarily made use of the water technique in the first season of the anime series, the movie Mugen Train makes us understand that the fire technique is Tanjiro’s innate ability. His father utilized this power to perform the Hinokami Kagura dance. 

Again, there could either be a Flame or Fire Hashira, not both. Since Rengoku was already the Flame Hashira, his continuous presence in the show would have impeded the protagonist, Kamado Tanjiro, from becoming the Fire Hashira.

Hence, Rengoku sadly needed to die to allow Tanjiro to reach his full potential and defeat Muzan.