Zenitsu receives a letter from home while training in Demon Slayer Hashira Training Arc

What’s in Zenitsu’s Letter from ‘Demon Slayer,’ Episode 7, Season 4?

Zenitsu has always been a fearful and flighty character in Demon Slayer. The only times we’ve seen him stiff and serious are during his fights, when he’s fast asleep. So why has Zenitsu gone serious in episode 7 of Demon Slayer’s latest season?

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The contents of Zenitsu’s letter weren’t shown in the anime, but the manga gives us further context of what scared Zenitsu straight. Believe it or not, it’s actually related to Gyomei Himejima’s backstory. Simply put, Zenitsu’s grandfather and master, Jigoro Kuwajima, ended his life after one of his former apprentices became a demon.

Chapter 144 of the Demon Slayer manga confirms this. The chapter shows Zenitsu confronting Kaigaku, who became a demon. Zenitsu, who was often cowardly, changed after learning of the way Kuwajima died. It was a slow and painful death, and nobody was around to put Zenitsu’s grandfather out of his misery. The demon, despite becoming exceedingly talented, did not care for the old man’s death.

Kaigaku is a consistent traitor

Ironically, Kaigaku was the same child in Himejima’s story. The current Stone Hashira told Tanjiro about how he once took care of orphans in his former temple. One night, a child came home too late and encountered a demon. Kaigaku betrayed Himejima and the rest of the children in exchange for his own life.

Kaigaku, who became homeless after the incident, was taken under the wing of Kuwajima. As the former Thunder Hashira, Kuwajima trained both Kaigaku and Zenitsu as his disciples. Zenitsu could only use the first form of Thunder Breathing, while Kaigaku was able to use all the other forms except the first. Because of this, Kuwajima named both Zenitsu and Kaigaku as his successors instead of naming only one.

Throughout the series, Zenitsu has never been a character with guts. The death of his master gave him more courage, and you’ll see that he no longer needs to fight while sleeping. As tragic as the circumstance is, Zenitsu became much stronger because of it.

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Vanessa Esguerra
Vanessa Esguerra (She/They) has been a Contributing Writer for The Mary Sue since 2023. After graduating with a Bachelor of Arts in Political Economy, she (happily) rejected law school in 2021 and has been a full-time content writer since. Vanessa is currently taking her Master's degree in Japanese Studies in hopes of deepening her understanding of the country's media culture in relation to pop culture, women, and queer people like herself. She speaks three languages but still manages to get lost in the subways of Tokyo with her clunky Japanese. Fueled by iced coffee brewed from local cafés in Metro Manila, she also regularly covers anime and video games while queuing for her next match in League of Legends.