Zenitsu Agatsuma is not the bravest person out there. You don’t need to be the biggest fan of Demon Slayer to pick up on that. The anxious young man often expresses fear and reluctance whenever he faces danger. He can only unlock his true combat abilities and fight demons while unconscious, or in a state of extreme fear.
Despite wielding the Thunder Breathing Style and specializing in lightning-fast sword techniques, Zenitsu is exceptionally timid. However, this carefree demon slayer’s journey takes a dramatic turn in season 4, episode 7. After receiving a mysterious letter carried by Chuntaro, his bird, his demeanor changes. Just what was in that letter that was serious enough to cause Zenitsu to change?
What was in the letter?
While it has yet to be revealed in the anime, chapter 144 of the Demon Slayer manga reveals that the letter contained the tragic fate of Zenitsu’s master and grandfather, Jigoro Kuwajima.
Jigoro was the former Thunder Hashira and had trained Zenitsu in Thunder Breathing. Sadly, he committed Seppuku due to the actions of his former student Kaigaku, who strayed from the path of demon slayers. Kaigaku turned into a demon, and joined the Upper Moon ranks, which is highly frowned upon. But what this also meant is that Jigoro’s training of a Thunder Breathing user ultimately led to Kaigaku using his skills for evil under Muzan’s influence. Tragically, Jigoro’s Seppuku was without a decapitator, indicating he endured immense pain before dying, as there was no one to end his suffering swiftly.
What happened to Zenitsu in Demon Slayer?
After reading the aforementioned letter, Zenitsu’s attitude immediately changes. He also ignores Tajiro Kamado, evidently propelled by a personal quest. Although it’s clear that the news of his master’s death devastates Zenitsu, it also ignites a profound and remarkable change in him. His carefree and often fearful demeanor shifts to a resolute determination to honor his master’s legacy, and confront Kaigaku.
Just like his grandfather, Zenitsu blames himself for Kaigaku’s defection. He believes his presence and abilities contributed to Kaigaku’s insecurity and eventual betrayal, especially since Kaigaku could never learn Thunder Breathing First Form. Vowing to uphold his master’s honor, Zenitsu adopts a more serious and focused attitude, setting aside his fears to take on the challenges ahead.
This character development marks a significant evolution for Zenitsu, who transitions from a timid, comic-relief character, into a more mature and determined warrior. His journey therefore becomes a path of redemption and duty, driven by a deep sense of responsibility and respect for his late master. This pivotal moment not only shapes Zenitsu’s future actions, but also enriches his role within the Demon Slayer narrative.