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Get out of here... You gonna make me repeat myself?, leave my sight. You know why. The way you cry like a baby all day long. Aren't you ashamed of yourself?.. Good for nothing, any effort spent on you is an absolute waste of time. Our teacher is an extraordinary man. [..] Hey you, don't go being all familiar and calling him gramps! He's a former Hashira, someone who earned the highest tile in the Demon Slayer Corps. Hardly anyone ever gets the chance to be trained by a former Hashira. The time he spends training you is all for nothing its infuriating to see! I hate even looking at you so get out! Why are you even here? Why do you insist on clinging on like a patch of mold?!
~ Kaigaku berates Zenitsu in the past.
I know what right and wrong is! Those who appreciate my talent is the right, those who don't and denounce me is the wrong!
~ Kaigaku reveals his values.

Kaigaku (獪岳,かいがく) is a minor antagonist in the Demon Slayer: Kimetsu no Yaiba manga and anime. He was a member of the Twelve Kizuki, holding the position of Upper Rank Six after the deaths of Daki and Gyutaro. He serves as a supporting antagonist in the Infinity Castle Arc.

He was originally a Demon Hunter and member of the Demon Killing Corps as well as Zenitsu Agatsuma's senior student when they were being taught by Jigoro Kuwajima. After his treachery, Kaigaku later becomes Zenitsu's archenemy. His cowardice would later lead him to his downfall when Zenitsu overcomes his insecurities as Kaigaku mocks Jigoro. Kaigaku's Thunder Breathing training would lead to his Blood Demon Arts being related to lightning.

He is voiced by Yoshimasa Hosoya in the Japanese version of the anime and by Alejandro Saab in the English version, the former of which also voiced Wave from Akame Ga Kill! and Reiner Braun from Attack on Titan.


I always side with those who properly acknowledge me, whenever and at any time.
~ Kaigaku to Zenitsu at their reunion, displaying his opprtunistic tendency.

Although diligent, Kaigaku is an arrogant opportunist who follows strong and despises the weakness, especially when it obstructs something he wants, as seen with his bullying words against Zenitsu.

Deep down, Kaigaku is also a coward, who cowered in fear at Kokushibou and knelt in front of him, willingly accepting Muzan Kibutsuji's blood and became a demon as a result. Kaigaku also shows no remorse for his own treachery and cowardice, even teasing his master, Jigoro Kuwajima, as a worthless weakling just like Zenitsu after discovering the latter committed suicide out of shame.


Early life

Kaigaku was an orphan and a thief, who had to eat scraps and steal to survive. This established a certain belief in his head, he started to believe that strength was the only thing worth respecting, and those who can‘t see true strength or are too weak aren’t worth respect.

First Treachery

When he was a child, Kaigaku was one of the orphans Gyomei Himejima cared for at his temple, and had rely on theft and eating scrap to survive. However, he had developed a self-serving view upon survival. After he was caught by the other children for stealing temple money, he was chased out at night. After that, Kaigaku encountered a Demon, which he then let into the temple in exchange for having his life spared, in order to seek revenge against Gyomei and other children. It eventually caused Gyomei to be wronged and sent into prison, until he had been rescued and joined the Demon Slayer Corps.

Second Treachery

After acknowledging the Demons' existence, Kaigaku decided to become a Demon Slayer in order to become strong. During his career as a Demon Slayer, Kaigaku was taken in by Jigoro Kuwajima, the Thunder Pillar, along with Zenitsu, and taught the Breath of Thunder style. Kaigaku became determined to become Jigoro Kuwajima’s successor and the new Thunder Pillar. However, Kuwajima revealed that Zenitsu would become his successor, since Zenitsu had potential to master the First Form of Thunder Breathing, while Kaigaku had never mastered it even after mastering the other Forms from the Second to the Sixth.

Believing he was losing his master's favor, Kaigaku began to despise Zenitsu for being merely a weak and timid man who earned his master's favor out of dumb luck. Thus, he started to bully Zenitsu constantly.

Later on, Kaigaku went on a solo mission to hunt down Kokushibou, the Upper Moon One, but was overpowered. After the defeat, Kaigaku kneeled before Kokushibo and begged for his life. Kokushibo offered Muzan's blood to turn Kaigaku into a demon, which Kaikagu accepted, causing his transformation into a man-eating savage. After finding out that his student betrayed him and renounced humanity, Kuwajima committed seppuku out of shame.

Infinity Castle Arc

After the deaths of Daki and Gyutaro, Kaigaku was promoted to become Upper Moon Six of the Twelve Demon Moons due to his power and confronted Zenitsu as a rematch he always desired. Zenitsu revealed his master's demise to his teacher's classmate, accusing Kaigaku for the one to blame, but Kaigaku nonchalantly disagreed with his former classmate, believing that those who praise him were good and those who don't were evil. To make matters worse, Kaigaku didn't care about his master's death for ignoring him. Disgusted, Zenitsu called Kaigaku a piece of trash who can never master Thunder Breathing - First Form, and decided to part ways with his former prefect.

Since Kaikagu had yet to master his Demon Skills fully, Zenitsu ultimately won the duel with his newest technique, Thunder Breathing: Seventh Form: Flaming Thunder God. Kaigaku mockingly commented that their master does favor Zenitsu more for teaching him that style, until Zenitsu revealed that Flaming Thunder God was his own making, in order to fight alongside Kaigaku as equals.

Hearing this, Kaigaku watched in shock and anger as his old classmate was saved by Yushiro. Eventually, Kaigaku's head screamed in anger as he disintegrated. Yushiro scornfully declared that Kaigaku will be given nothing since he never learned how to give, and Kaigaku's die-alone fate was sealed once he decided to let his desire inflate and take him over.

Powers and Abilities

Blood Demon Art (血鬼術 Kekkijutsu):

  • Electricity Manipulation: Complementing his breathing and combat style, Thunder Breathing, Kaigaku can use his Blood Demon Art to generate and manipulate electricity. Kaigaku mainly infuses electricity with his swordsmanship to enhance the power of his attacks and to make up for his inability to perform its simplest technique: First Form: Thunderclap and Flash. Furthermore, his electricity has been demonically enhanced, creating a gash that cracks his opponent's flesh and burns it, greatly augmenting the lethality of his attacks. This also turns the electricity he manipulates a deep shade of black. To make matters worse, the cut made by Kaigaku's Blood Demon Art expands and spreads onto other body parts. Had Zenitsu not having the fortune to encounter Yushiro who had medical knowledge in time, the former would have died from his wounds.
  • Thunder Breathing (雷の呼吸 Kaminari no kokyū):

Kaigaku was taught by a former Hashira, Jigorō Kuwajima in the usage of this Breathing Style and immediately stuck out as a natural prodigy due to having mastered it easily. But despite his natural talent, Kaigaku was was unable to learn the first form of the Breathing Style despite learning the other styles of the Thunder Breathing.

  • Second Form: Rice Spirit (弐ノ型 稲魂 Ni no kata: Inadama) - Kaigaku unleashes five electrified arching slashes all in a single moment. Interestingly, Inadama is also his surname (revealed in Kimetsu Academy)
  • Third Form: Thunder Swarm (参ノ型 聚蚊成雷 San no kata: Shūbun Seirai) - Kaigaku surrounds his target with powerful waves of electricity and sword slashes that slice up the enemy in all directions.
  • Fourth Form: Distant Thunder (肆ノ型 遠雷 Shi no kata: Enrai) - Kaigaku generates powerful lightning strikes in several directions with his blade from a far distance, effectively turning his sword into a makeshift gun.
  • Fifth Form: Heat Lightning (伍ノ型 熱界雷 Go no kata: Netsu Kairai) - Kaigaku unleashes a powerful ranged electrified sword slash upwards that burns the flesh of his target.
  • Sixth Form: Rumble and Flash (陸ノ型 電轟雷轟 Roku no kata: Dengō Raigō) - One of the most powerful Thunder Breathing techniques. Kaigaku releases a series of powerful ranged electricity attacks that strike his opponent from multiple directions.



  • Kaigaku may be similar to Pigma Dengar from the Star Fox series due to his betrayal leading to his original superior's demise. However, Kaigaku's betrayal leading to Jigoro's demise was an indirect one as well as confirmed, while Pigma deliberately tried to make his own superior, James McCloud die but may have failed.
  • Kaigaku's name (獪岳) contains the following symbols: Kai (獪) meaning wily or sly and Gaku (岳) meaning big mountain. Combining those letters together, it is roughly translated as 'a man who deludes himself to be as bigger than he really is', hinting at his ego.
  • As his archenemy Zenitsu was only able to use the First Style of Breath of Thunder, other styles of Breath of Thunder were not revealed until Kaigaku used them. But other styles used by Kaigaku are not likely to be their original styles since Kaigaku is now a Demon with an ability to use a Blood Demon Art. Therefore other styles used by Kaigaku are likely to have been corrupted.
  • Kaigaku and Kokushibo are the only known demon slayers to have become demons themselves. Coincidentally, Kokushibo makes Kaigaku a Demon with his own blood upon defeating him in battle.

External Links


           Kimetsu no Yaiba logo.svg Villains


Demon King
Muzan Kibutsuji

Twelve Demon Moons
Original Upper Moons †
One: Kokushibou † | Two: Doma † | Three: Akaza † | Four: Hantengu † | Five: Gyokko † | Six: Daki † & Gyutaro

Replacement Upper Moons †
Four: Nakime † | Six: Kaigaku

Lower Moons †
One: Enmu † | One: Ubume (past) † | Four: Mukago † | Five: Rui † | Six: Kyogai (replaced) † Second: Hairou (past) † |

Muzan's Lesser Followers †
Susamaru and Yahaba † | Hand Demon † | Swamp Demon † | Spider Family † (Father Spider † | Mother Spider † | Brother Spider † | Sister Spider †) | Snake Demon

Tengan Uzui's Father | Iguro Family | Doma's Parents | Kanao Tsuyuri's Parents