Is Kaigaku Related to Zenitsu? The Truth Behind Their Rivalry

If you are a fan of the popular manga and anime series Demon Slayer: Kimetsu no Yaiba, you might have wondered about the relationship between two of the characters: Zenitsu Agatsuma and Kaigaku. These two are both users of the Thunder Breathing style, but they have a very different personality and attitude towards life. Zenitsu is a timid and cowardly boy who often cries and faints in fear, but he has a hidden talent that allows him to unleash his full potential when he is unconscious. Kaigaku, on the other hand, is a ruthless and arrogant man who became a demon in order to gain more power and joined the Twelve Kizuki, the elite group of demons under the command of Muzan Kibutsuji, the main antagonist of the series. Kaigaku and Zenitsu have a bitter rivalry that stems from their past, and their final confrontation is one of the most intense and emotional battles in the story. But are they related by blood? What is the origin of their conflict? And what is the meaning of their names? In this article, we will explore these questions and reveal the truth behind their rivalry.

The Origin of Their Conflict

According to Kimetsu no Yaiba Wiki, Zenitsu and Kaigaku have a common history because they were both disciples of Jigoro Kuwajima, the former Thunder Hashira (Pillar), who was one of the strongest and most respected Demon Slayers in history. Jigoro was a kind and compassionate master who taught them the Thunder Breathing style, which is one of the five original breathing styles derived from the Sun Breathing, the first and most powerful breathing style ever created. However, Zenitsu and Kaigaku had very different experiences under Jigoro’s tutelage. Zenitsu was an orphan who was sold to Jigoro by his abusive relatives. He was grateful to Jigoro for taking him in and treating him like a son, but he also suffered from low self-esteem and lack of confidence. He was constantly bullied by Kaigaku, who mocked him for being weak and useless. Kaigaku was also an orphan who was taken in by Jigoro, but he had a different attitude towards his master. He was ambitious and greedy for power, and he only respected Jigoro for his strength. He looked down on Zenitsu and anyone else who he deemed inferior to him. He also resented Jigoro for not teaching him the secret technique of the Thunder Breathing style, which is only passed down to one successor per generation.

The conflict between Zenitsu and Kaigaku reached its peak when they were sent to undergo Hashira Training, a rigorous training program designed to prepare Demon Slayers for becoming Hashira, the highest rank in the organization. During this training, Kaigaku encountered Kokushibo, the Upper Rank One of the Twelve Kizuki, who was also a former Demon Slayer and a user of the Moon Breathing style, which is another derivative of the Sun Breathing style. Kokushibo offered Kaigaku to become his subordinate and turn into a demon, promising him more power and longevity. Kaigaku accepted his offer without hesitation, betraying his master and comrades. He also killed several Demon Slayers who tried to stop him, including his fellow Thunder Breathing user Himejima Goto. When Jigoro learned about Kaigaku’s betrayal, he was devastated and ashamed. He decided to commit seppuku (ritual suicide) as a way of taking responsibility for his failure as a master. He left behind a letter for Zenitsu, apologizing for his death and entrusting him with his Nichirin Sword and his earrings, which were symbols of his lineage as a successor of the Thunder Breathing style. He also expressed his hope that Zenitsu would become a great Demon Slayer and protect people from demons.

Zenitsu was heartbroken by Jigoro’s death, but he also inherited his will and determination. He vowed to honor his master’s memory by becoming stronger and fulfilling his duty as a Demon Slayer. He also developed a deep hatred for Kaigaku, whom he blamed for causing Jigoro’s death and dishonoring his legacy. He swore to kill him someday and avenge his master.

The Final Confrontation

Zenitsu’s chance to face Kaigaku came during the Infinity Castle Arc, which is the final arc of the manga series. In this arc, the Demon Slayer Corps launched an all-out assault on Muzan’s fortress, where they encountered the remaining members of the Twelve Kizuki. Among them was Kaigaku, who had become the new Upper Rank Six after killing Daki and Gyutaro, the previous holders of that position. Kaigaku and Zenitsu sensed each other’s presence and sought each other out, eager to settle their score once and for all.

Their battle was a clash of thunder and lightning, as they both used the Thunder Breathing style to attack each other. However, Kaigaku had an advantage over Zenitsu, as he had also developed a Blood Demon Art that enhanced his Thunder Breathing techniques with demonic energy. He also taunted Zenitsu for being weak and pathetic, and for not being able to use anything other than the First Form of the Thunder Breathing style, which is called Thunderclap and Flash. Zenitsu, however, remained calm and focused, and revealed that he had mastered the secret technique of the Thunder Breathing style, which is called Honoikazuchi no Kami (God of Thunderclap and Flash). This technique allows the user to perform the First Form at an extremely high speed and frequency, creating multiple flashes of lightning that strike the enemy from different angles. Zenitsu used this technique to overwhelm Kaigaku and cut off his head, ending his life.

As Kaigaku was dying, he expressed his regret for becoming a demon and betraying Jigoro. He also admitted that he was jealous of Zenitsu for being chosen as Jigoro’s successor and inheriting his earrings. He asked Zenitsu to forgive him and to take his sword as a souvenir. Zenitsu refused to forgive him, but he also felt sorry for him. He told him that he should have been proud of being Jigoro’s disciple, and that he should have lived a better life. He also told him that he hated him, but he also loved him as a brother. He then prayed for his soul to rest in peace.

The Meaning of Their Names

According to Fiction Horizon, the names of Zenitsu and Kaigaku have some interesting meanings and connections. Zenitsu’s name consists of two kanji characters: 善 (zen), which means “good” or “virtue”, and 逸 (itsu), which means “to deviate” or “to excel”. His name can be interpreted as “one who deviates from goodness” or “one who excels in goodness”, depending on the context. This reflects his dual personality: on one hand, he is a cowardly and selfish person who often runs away from danger and tries to avoid responsibility; on the other hand, he is a brave and noble person who fights with all his might to protect others and uphold his ideals.

Kaigaku’s name also consists of two kanji characters: 獪 (kai), which means “cunning” or “ferocious”, and 岳 (gaku), which means “peak” or “mountain”. His name can be interpreted as “one who is cunning and ferocious like a mountain” or “one who reaches the peak of cunningness and ferocity”. This reflects his personality: he is a ruthless and arrogant person who seeks power and glory at any cost, even if it means betraying his master and comrades.

Another interesting connection between their names is that they both contain the same radical (部首 bushu), which is 厂 (an), meaning “cliff”. This radical is also present in the name of Jigoro Kuwajima, their master, whose name consists of three kanji characters: 桑 (kuwa), meaning “mulberry”, 家 (ji), meaning “house” or “family”, and 島 (shima), meaning “island”. His name can be interpreted as “the family of the mulberry island” or “the island of the mulberry house”. The radical 厂 (an) in his name is part of the character 島 (shima), which means “island”. This suggests that Jigoro was like an island for Zenitsu and Kaigaku, a place where they could find shelter and guidance. However, they both left this island in different ways: Zenitsu left to pursue his duty as a Demon Slayer, while Kaigaku left to join the demons.


Zenitsu and Kaigaku are not related by blood, but they have a complex relationship that spans from friendship to rivalry to hatred. They were both disciples of Jigoro Kuwajima, the former Thunder Hashira, who taught them the Thunder Breathing style. However, they had very different personalities and goals in life: Zenitsu was timid and kind-hearted, while Kaigaku was ruthless and power-hungry. Their conflict escalated when Kaigaku became a demon and joined the Twelve Kizuki, causing Jigoro to commit suicide. Zenitsu inherited Jigoro’s will and sword, while Kaigaku inherited his earrings. They finally faced each other in a fierce battle in the Infinity Castle, where Zenitsu emerged victorious using the secret technique of the Thunder Breathing style. As Kaigaku died, he expressed his remorse and envy

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