Demon Slayer: Does Zenitsu have a brother?

Taking a look at whether or not Zenitsu has a brother in the series (Image via Koyoharu Gotouge/Shueisha, Viz, Demon Slayer)
Taking a look at whether or not Zenitsu has a brother in the series (Image via Koyoharu Gotouge/Shueisha, Viz, Demon Slayer)

Zenitsu Agatsuma is one of the main characters of the Demon Slayer series whose popularity has skyrocketed ever since the release of the first few episodes. He is someone who practices Thunder Breathing and is a valued member of the Demon Slayer Corps. He has played a pivotal role in defeating some of the toughest demons in the series.

Fans are curious to know if this character has a brother in the series. Let’s take a look at Zenitsu’s past and trace his journey throughout the series.

Disclaimer: This article contains major spoilers from the manga.

Understanding whether or not Zenitsu has a brother in the Demon Slayer series

Zenitsu Agatsuma is one of Jigoro Kuwajima’s disciples who is learning the Thunder Breathing technique in an attempt to become a demon hunter. He then passed the Final Selection and joined the organization. Jigoro acted as Zenitsu’s adoptive guardian in the series and decided to train the young man to become a fine swordsman. Despite Zenitsu’s cowardice and constant whining, Jigoro never lost hope in him and made a fine demon hunter out of him, who even managed to defeat an Upper Moon demon all by himself.

One of the characters that people mistake for Zenitsu’s brother in the series is Kaigaku. However, this is not true, and Kaigaku is just his senior in the dojo where the two trained under the guidance of Jigoro, and was also adopted by the former Thunder Hashira. There was a lot of animosity between these characters because Kaigaku always looked at Zenitsu as a coward. Despite that, Zenitsu was also elected as the successor of the dojo alongside Kaigaku. This irritated Kaigaku, and he was rude to Zenitsu quite often in Demon Slayer.


However, everything changed after a certain event that would take place in the Hashira Training arc of the Demon Slayer series. It was at this stage that Kaigaku encountered Kokushibo and lost to him. In order to save himself, he begged the demon to spare his life, and became a demon after Muzan's blood was given to him. He became the new Upper Moon 6 demon and, because of this, Jigoro killed himself by committing Seppuku. This agonized Zenitsu, and he confronted Kaigaku later in the series.

During this encounter, Kaigaku was unapologetic and even managed to insult his former master in Zenitsu’s presence. This angered Zenitsu, and he was a different person when he fought his former senior. Not only did Zenitsu fight the demon while being completely conscious, he also retorted to Kaigaku’s comments which took him by surprise. It was during this fight that Zenitsu managed to create a new form in Thunder Breathing that was unique to him. He managed to beat Kaigaku with ease and avenged Jigoro Kuwajima’s death in the Demon Slayer series.

This hurt Zenitsu because Kaigaku was someone he trained with all his life. He might not have liked Kaigaku because he was rude, but he certainly respected Kaigaku a lot as a combatant. Zenitsu respected him because he was a skilled swordsman and looked up to him. But nowhere in the manga was it mentioned that Kaigaku was Zenitsu’s blood relative. However, this could be understandable because of their relationship and constant bickering.

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