Updated on June 30, 2:20 p.m. (GMT+8): Amended Zenitsu’s relationship with Jigoro Kuwajima.

Zenitsu Agatsuma, the blonde swordsman known for his flashy techniques and sleepy demeanor, faces a new challenge in Demon Slayer season 4 episode 7.

The Thunder Breath user receives the devastating news that ultimately changes him forever. This revelation sets him on a new path fueled by a potent mix of grief and determination.

Demon Slayer llustration provided by ufotable for the third episode of the Pillar Training Arc of the TV anime "Demon Slayer: Kimetsu no Yaiba", "Tanjiro Fully Recovered!! Fully Participates in Pillar Training"
Credit: ufotable, Shueisha, Koyoharu Gotouge, ONE Esports
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What could shake Zenitsu to his core and ignite a fire within the usually drowsy swordsman?

We’re going to answer this question for all the Demon Slayer Zenitsu stans.

Warning: Major spoilers for those who haven’t read the Demon Slayer manga.

What shocked Zenitsu Agatsuma in Demon Slayer season 4 episode 7?

Demon Slayer main character Zenitsu Agatsuma seen crying in season 4 episode 6
Credit: ufotable, Shueisha, Koyoharu Gotouge

In episode 7, titled “The Stone Hashira Gyomei Himejima,” Zenitsu’s demeanor noticeably shifts. His usual carefree attitude vanishes, replaced by a newfound seriousness and focus.

He even brushes aside Tanjiro Kamado‘s concerns, driven by a personal mission he refuses to share.

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This change stemmed from a devastating revelation delivered by his sparrow, Chuntaro. The letter conveyed the news that Zenitsu’s former master, Jigoro Kuwajima, the former Thunder Hashira, had passed away.

Kuwajima wasn’t just any mentor. He was the master swordsman who trained Zenitsu in the art of Thunder Breathing.

Out of compassion, Kuwajima helped Zenitsu financially. The former Hashira took Zenitsu under his wing, providing him with food, shelter, and a new purpose.

However, Zenitsu wasn’t Kuwajima’s only student. Among them was Kaigaku, a timid child who ultimately strayed from the path of the Demon Slayers.

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The news of Kaigaku’s descent into darkness heavily affected Kuwajima. Wracked with shame, the former Thunder Hashira took his own life and committed seppuku, a slow and agonizing form of suicide. Zenitsu learned that his former master bled out without the honor of a quick death.

Kaigaku appeared in a flashback scene during season 4 episode 7. The manga revealed that Kaigaku was the child responsible for letting a demon into the temple of the Gyomei Himejima before he became the Stone Hashira. This incident resulted in the deaths of seven other children and Himejima’s near-execution.

Demon Slayer Mugen Train arc key visual in ONE Esports featured image for article "Demon Slayer Arcs — a comprehensive list"
Credit: ONE Esports, uftotable, Koyoharu Gotouge
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The manga shed further light on Kaigaku’s fate. He quickly rose through the Twelve Demon Moons (Twelve Kizuki) ranks, becoming Upper Rank Six.

Kaigaku replaced Daki and Gyutaro, the demons defeated by the combined efforts of Sound Hashira Tengen Uzui, Inosuke Hashibira, Zenitsu, and the Kamado siblings, Tanjiro and Nezuko in season 2’s Entertainment District arc.

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