Hi there, Junko from Japan here! Does Zenitsu have a brother? No, he doesn’t have any blood-related family. Zenitsu was an abandoned child and was all alone.
But he has a senior apprentice with whom learned the Thunder Breathing together from Kuwajima Jioro, Zenitsu’s master he called “JICHAN (grandpa).”
The name of the fellow apprentice is KAIGAKU. Grandpa, Kaigaku, and Zenitsu lived together, and Kaigaku was substantially a brother to Zenitsu.
What Kind of Person Is Kaigaku?
Kaigaku is also an orphan. He was a hard worker while Zenitsu often skipped the Thunder Breathing training. So Kaigaku hated Zenitsu and was hard on him. Zenitsu also disliked him but still respected his talent and attitude as a swordsman.
Later, these two will take the opposite path.
Warning: Spoilers
The content below contains spoilers. Scroll the page only when you’re okay with that!
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The Battle against Kaigaku at the Mugen Castle
In the last part of Demon Slayer, Kaigaku appears in front of Zenitsu as one of the Twelve Kizuki demons.
Kaigaku joined the Demon Slayer Corps in advance of Zenitsu and came across Kokushibo during his mission. He was defeated by Kokushibo but accepted his offer and became a demon. Kaigaku couldn’t resist the fear of death.
Whether good or bad, Kaigaku adapted Muzan’s blood and successfully became a demon. After that, he was assigned to the Upper Moon Six of the Twelve Kizuki since the position was vacant because of the death of Gyutaro and Daki.
Since a demon came from his own school, Kuwajima chose his own death to take responsibility. He comitted SEPPUKU and died. I think seppuku is known as HARAKIRI in foreign countries.
Usually, the ritual of Seppuku requires a Samurai who specializes in cutting the head off just after the convict cut his belly with a Katana. This Samurai was called KAISHAKU and carried out their job to reduce the pain of the convicts.
But Zenitsu’s grandpa didn’t attend any Kaishaku and died while suffering. It seems he committed Seppuku alone on purpose and accepted the pain to take responsibility as a Kaigaku’s master.
Grandpa’s death was all because of Kaigaku. Yet he didn’t show any regret and even insulted his master. Zenitsu got furious about that and faced him at the Mugen Castle. Though Kaigaku took advantage of the battle first and gave Zenitsu fatal wounds, he ended up being defeated with Zenitsu’s final secret technique.
After the battle was settled, Zenitsu lost consciousness and saw grandpa in his dream. He was shedding tears and praised him saying “Zenitsu, I’m proud of you.”
For your information, Zenitsu and his grandpa were standing across the river from each other. I think this river is the Sanzu River in Buddhism. We learn that we all cross the Sanzu River when we die and go to the other world. Once you cross it, you’ll never be able to return to this world.
When Zenitsu tried to cross the river to see his grandpa, some flowers got entangled in his legs and stopped him. I guess that happened because Kuwajima denied Zenitsu’s death and put him back into the living world.
We sometimes hear similar stories of near-death experiences in which you tried to cross the river but were rejected by your family or familiar people. Most Japanese people believe in Buddhism, and we consider the river the Sanzu River.
Why Did Kaigaku Hate Zenitsu So Much?
Kaigaku didn’t like Zenitsu because he was lazy and easily ran away from the Thunder Breathing training, yet Kuwajima took care of him well.
Kaigaku regarded Zenitsu good-for-nothing since he could use only the first form of Thunder Breathing. On the other hand, Kaigaku could never use the first form while he mastered all other forms.
Kuwajima tried to make Kaigaku and Zenitsu together succeed in the Thunder Breathing. But Kaigaku couldn’t admit that he and a failure were rated the same. He was always dissatisfied with his situation and thought that Zenitsu was overrated.
Kuwajima loved and treated both of them equally, but Kaigaku never understand his feelings until the very end.
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