Hi, Junko from Japan here! Zenitsu fights Kaigaku in chapters 143 to 146 in the original manga version of Demon Slayer. It’s printed in a comic book vol. 17.
Here are summaries for each chapter. I added some information about Japanese culture such as seppuku (harakiri) and the river for the dead. Hope it helps you to understand and enjoy Demon Slayer more deeply.
Note: I’m writing this post based on my Demon Slayer comics which are all in Japanese. I translated the chapter titles by myself, and they may be different from the ones in the official English edition. Sorry if you’re confused!
143 Ikari: Anger
Zenitsu came across Kaigaku at the Mugen Castle where the final battle against Kibutsuji Muzan vs Demon Slayer Corps began. Demon Slayer Corps challenged all-out battle, but the swordsmen including the Hashira members got scattered by Nakime’s Demon Blood Art that controlled the Mugen Castle.
There they confronted their nemesis demons. For Zenitsu, it was Kaigaku who became a demon and caused his “Jiichan (grand-pa)”‘s death.
Kaigaku was placed on the Upper Rank 6 instead of Gyutaro and Daki. Zenitsu declared war upon him saying “I no longer consider you my senior apprentice.”
144 Uketsugu mono tachi: Those who inherit
Zenitsu told Kaigaku how their master, Kuwajima Jigoro, died. He committed SEPPUKU and died alone to take responsibility for the fact that his apprentice became a demon.
I think SEPPUKU is known as “harakiri” in foreign countries. It’s one of the death penalties for Samurai warriors. A sentenced Samurai pierce his belly with a Katana sword.
Usually, a sentenced one has a supporter called KAISHAKU. A Kaishaku is a specialist who cuts a head off from a body. The instant a sinner pierce his belly, a Kaishaku cut his head down to ease his pain and lead to an easy death.
However, Kuwajima didn’t have a Kaishaku (probably on purpose) and died a painful death, which made Zenitsu despaired and furious.
Kaigaku showed no regret about the fact and even insulted his master. Before becoming a demon, Kaigaku had held a grudge against Kuwajima because he nominated both Kaigaku and Zenitsu as the Thunder Breathing joint successor.
Kaigaku had looked down on Zenitsu and believed that he was much superior. Yet Kuwajima treated them equally, which made him quite unsatisfied.
In this scene, the fact that Kaigaku couldn’t use the Thunder Breathing’s first form was also revealed by Zenitsu.
Kaigaku performed the Thunder Breathing forms enhanced with his Demon Blood Art one after another. Zenitsu got injured but stayed determined to fight.
145 Shiawase no hako: Box of happiness
The match was decided in a split second. Zenitsu performed the seventh form of Thunder Breathing, HONO IKAZUCHI NO KAMI (flaming thunder god), and cut Kaigaku’s head off in one slash.
Hono Ikazuchi no Kami was the original form developed by Zenitsu. He mastered the first form Hekireki Issen and evolved it into the new form. Zenitsu told Kaigaku:
“This is my form. My only form I developed.”
“With this technique, I wanted to fight beside you someday…”
Both Kaigaku’s head and heavily injured Zenitsu started to fall down toward the bottom of the Mugen Castle.
146 Hokori: Pride
Kaigaku’s head was still conscious, but his mind was full of envy. No compassion, and no regret to become a demon and betrayed his master.
There Yushiro appeared to rescue Zenitsu from falling down. He found Kaigaku’s head collapsing and despised him.
“Those who only desire will end up with nothing. Since you can’t create anything on your own, it’s the same as having nothing.”
“How miserable to die alone.”
Personally, I love Yushiro’s sharp tongue!
On the other hand, Zenitsu lost consciousness and dreamt a dream in which he saw Jiichan standing across the river.
Zenitsu shouted and apologized about he couldn’t get along with Kaigku, but Kuwajima stayed silent. Zenitsu tried to cross the river to get closer to his Jiichan (grandpa), but the Higanbana flowers got entangled in his feet and blocked him from proceeding.
Then, Kuwajima finally spoke to him in tears.
“Zenitsu, you are my pride.”
I shed tears too 😭. I think this is one of the most touching scenes in Demon Slayer.
After that, Zenitsu regained consciousness. The battle between brother apprentices resulted in Zenitsu’s win.
The river he saw is probably the SANZU NO KAWA, meaning the Sanzu River. Buddhism teaches you’ll cross the Sanzu River when you die. That means you can’t get back to this world once you cross it.
Maybe Kuwajima denied him coming, and that’s why the Higanbana flowers prevented Zenitsu from moving. For your information, the word HIGAN represents “other world” in Buddhist terms.
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How Did You Like It?