We will discuss Kokushibo’s backstory from Demon Slayer: Kimetsu No Yaiba in this blog post. Kokushibo is the second strongest demon in Demon Slayer, just behind Muzan, the Demon King.

He is shy, quiet, and distant, giving off an air of unsettling calm and mystery that fits with his status as Upper Rank One.

He doesn’t talk much, but when he does, he speaks slowly and loudly, which gives his words more weight and authority. Kokushibo sticks to the rules and is always on time.

At the Upper Rank gathering, it was clear that he had a lot of respect for the Twelve Kizuki’s hierarchy.

Kokushibo Backstory | by EDIPTUS
Kokushibo Backstory | by EDIPTUS

Here, we will see Kokushibo’s backstory in Demon Slayer: Kimetsu no Yaiba. Kokushibo is one of the main characters in Demon Slayer, and it would be interesting to read his backstory in the story.

Kokushibo Backstory – As a Child

Born in the Sengoku Period, Kokushibo’s birth name was Michikatsu Tsugikuni.

When he and his brother Yoriichi were born, twins were seen as a bad sign, and when their father saw that Yoriichi had a strange birthmark on his forehead, he said he would kill Yoriichi.

Kokushibo Backstory as a child
Kokushibo Backstory as a child from Wiki

But when he told their mother, Akeno Tsugikuni, what he would do, she was furious.

They made a deal that Yoriichi would be sent to the temple and become a priest when he turned ten instead of being killed.

Yoriichi and Michikatsu grew up in very different ways. Yoriichi has been locked in a three-tatami room away from the rest of the house and kept away from his brother. Michikatsu sneaked around behind their father’s back to see his brother. He felt terrible for Yoriichi. Everyone thought Yoriichi was deaf until he was seven. He clung to his mother’s side whenever Michikatsu saw her.

At some point, he gave Yoriichi a flute he’d made as a gift.

Michikatsu (Kokushibo) Realizing His Brother’s Talents

Around the time Michikatsu was seven, he was practising sword swings while his brother watched.

When Yoriichi spoke for the first time, he shocked Michikatsu. However, Michikatsu didn’t care when Yoriichi said he wanted to be a samurai like his brother. He knew Yoriichi would be sent to the temple when he was ten.

Kokushibo Backstory | The Flute
Kokushibo Backstory | The Flute

Still, Yoriichi continued to watch Michikatsu train, and one day, one of their father’s men offered to teach Yoriichi. Even though he only showed Yoriichi a basic stance, the boy could land four blows on a skilled man. Michikatsu was confused because he had never landed a blow before.

He begged his brother to teach him how he did it.

Michikatsu was disappointed that Yoriichi said he didn’t like fighting and no longer wanted to become a samurai.

Discovering the Breathing Style

Once, though, Yoriichi said that before he took a stance, he breathed deeply and checked his bone alignment, muscle contraction, and blood flow. This may have been an early version of the Sun Breathing style that Yoriichi would later adopt.

This conversation made Michikatsu realize that for Yoriichi, the bodies of living things were see-through. This made him want to master the blade even more.

As Michikatsu looked at the sword, he felt jealous of his brother, who he thought was wasting his natural physical talent.

He also worried that, since their father probably knew about Yoriichi’s huge potential, their roles would be switched, and he would be the one sent to the temple instead of Yoriichi.

Yoriichi knew this, too.

Michikatsu (Kokushibo) Hating his Little Brother, Yoriichi

The night their mother finally died from her illness, he went to Michikatsu’s room at 3 a.m. to tell him the news and say goodbye.

Michikatsu planned to leave for the temple before their father could make Yoriichi the family’s new leader. Yoriichi thanked his brother for giving him heart and fondly held the flute that Michikatsu had given him earlier.

Kokushibo Demon Slayer Mark
Kokushibo Backstory | Demon Slayer Mark

Michikatsu, on the other hand, was annoyed. He didn’t understand why Yoriichi would value a flute that couldn’t even play in tune.

He watched his brother leave without saying anything.

His jealousy of his brother only got worse when he read his mother’s diary after she died. It showed that Yoriichi had known everything about their mother’s illness, from when she would die to how her left side was getting weaker and had planned accordingly.

From then on, Michikatsu didn’t like Yoriichi, who he realized was not only physically talented but also smart. He wished for his brother to die. And for the next few years, he thought it was true when he didn’t hear from him.

Kokushibo Backstory – As an Adult

Ten years later, Michikatsu became a samurai and married a woman who gave birth to two of his kids.

Kokushibo as an adult
Kokushibo as an adult

One night, a Demon attacked his camp and left him as the only survivor. Yoriichi quickly killed the Demon and apologized for not being able to save his subordinates.

When Michikatsu saw the person he hated again, he was so jealous that he left his family. He became a Demon Slayer to train with Yoriichi.

He saw his brother try and fail to teach the other Demon Slayers his own breathing technique. Regardless, he changed them to fit their strengths and made the first breathing technique. During that time, he trained with a Wind Breathing user and improved his sword skills with them.

Creating his own Breathing Style and Demon Slayer Mark

Michikatsu eventually woke up a Demon Slayer Mark and created a breathing style called the Moon Breathing that was based on the Sun Breathing. Even though this was a big deal, it was still not as powerful as Yoriichi’s Sun Breathing.

Yoriichi and Kokushibo Demon Slayer
Yoriichi and Kokushibo | BY MCAshe

As a Demon Slayer, Michikatsu was often proud of how unique their generation was, but he was annoyed by his brother’s optimism when he brought up the fact that neither of them had a successor for their unique Breathing Styles, the Sun Breathing or the Moon Breathing.

Kokushibo Backstory – Becoming a Demon

Michikatsu didn’t think he could beat his brother, and he was afraid that those who awakened their Demon Slayer Marks would die. So, Muzan Kibutsuji persuaded him to become a Demon, and he took the name Kokushibo.

Since he used Breathing Style, it took him three days to fully change into a demon. Eventually, he became Upper Rank One of the Twelve Kizuki. He stayed at that rank for hundreds of years, and his original name was lost to history.

Not long after he turned into a demon, he killed the Oyakata who led his era of Demon Slayers and brought his head to Muzan.

His young son was left to lead the Demon Slayer Corps after he died.

Shortly after he turned into a demon, his leader Muzan met another Demon Slayer, Yoriichi.

Since Muzan already had him as a subordinate, he tried to kill his twin without any anger or power in him. Instead, Yoriichi was able to completely overwhelm the Demon King and nearly kill him.

Muzan barely escaped with his life and asked Kokushibo for help to get rid of Sun Breathing. Since Yoriichi was kicked out of the Corps, Muzan and Kokushibo were able to kill all the swordsmen who used the Breathing Style.

Yoriichi vs Kokushibo

Sixty years after becoming a Demon, he met Yoriichi for the last time.

Yoriichi was devastated by his decision to change, while Kokushibo was disgusted to see his younger twin now old and sick, and he was furious to learn that he was much older than 25 years old, which was the fate of all marked Demon Slayers.

Beyond this, Kokushibo wasn’t as angry to see him as he thought he would be.

Yoriichi’s tears confused Kokushibo because it was the first time he had shown emotion in front of him. As Yoriichi was still a Demon Slayer and wanted to get rid of his human past, he knew he had to kill his younger brother.

Kokushibo Backstory 
 Moon Breathing Style by Cathiane
Kokushibo Backstory | Moon Breathing Style by Cathiane

Even though he was old and seemed blind, Yoriichi’s fighting stance as he prepared to strike scared Kokushibo, who knew then that he still had a lot of skill and power.

Even though Yoriichi was holding his blade tight in anticipation, he had already struck and cut across his neck. Kokushibo was angry when he saw that his brother’s strength hadn’t changed at all, so he waited for a return strike, even though he knew it would kill him.

Yoriichi Dying of Old Age

Yoriichi never got the chance to cut Kokushibo’s head off in its entirety because he died of old age while standing up.

When Kokushibo saw that his brother Yoriichi had surpassed everything and was dying of old age instead of losing a battle, he became very angry.

Since Muzan couldn’t beat Yoriichi in a fair fight, Kokushibo’s one chance at a fair fight was gone, and his brother would never lose again. Because he felt like a loser, he was angry and cut Yoriichi in half, but in the process, he broke the flute he had given him when he was a child.

Kokushibo Backstory | Kokushibo and Yoriichi | by Palarien
Kokushibo Backstory | Kokushibo and Yoriichi | by Palarien

Seeing that he still thought highly of him after he changed, Kokushibo couldn’t help but shed a tear. He couldn’t break his bond with his brother, so he decided to keep the flute for himself.

Kokushibo had fought many Demon Slayers over the centuries.

Final Thoughts – Kokushibo Backstory

Kokushibo had one of the saddest backstories in Demon Slayer. He could never surpass his brother, his family was killed, and he could see how much his brother loved him while he hated him with the same intensity.

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About the Author

Logan Rane

Hey, I'm Logan, and I love anime and manga. I could talk about them all day, write about them non-stop, and watch them around the clock. I've watched hundreds of animes and read thousands of mangas at this point in my life - so you could say I'm pretty deep into it all.

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