Upper-Rank One: Kokushibo Muichiro, Genya, Sanemi Shinazugawa and Gyomei Himejima fought together against Kokushibo, though Muichiro and Genya were no match for him and were killed. Sanemi and Gyomei decapitated Kokushibo, but he successfully regenerated his head just as Akaza had.
Gyomei, along with Muichiro, Sanemi and Genya, had to take down Kokushibo.
The last member, Upper Moon Four Nakime, ends up being killed by Muzan Kibutsuji himself to stop the Dimensional Infinity Fortress from being controlled by his enemies.
Later, after being decapitated by two marked Hashira, Kokushibo is able to regenerate his entire head and successfully conquered death by beheading after being decapitated by Nichirin Swords, a feat considered impossible for demons and only accomplished by two other demons: Akaza and the Demon King himself.
As a transformed Demon Slayer, Kokushibo uses a breathing style known as "Moon Breathing" (月の呼吸, Tsuki no kokyū), which directly derives from Yoriichi's Sun Breathing. He dies while fighting a combined effort of Gyomei, Sanemi, Genya, and Muichiro, with the latter two dying from their wounds soon after.
Kokushibo was loyal to Muzan, acting as enforcer to the Twelve Kizuki. In return, Muzan sees him as a business partner, possibly due to his fanatic loyalty to him, being his strongest Demon and because the two were jointly responsible for almost exterminating Sun Breathing.
no. Yoriichi is not Tanjiro's dad, that would be Tanjuro. And Yoriichi is not related to the Kamado clan at all.
Some of the characters who have faced Yoriichi and survived
This happened due to a treatment that had gone wrong. While he was being treated, Muzan killed the doctor because he was not able to observe any results.
Unable to fight back, Doma realized he was tricked but it was too late. He was soon decapitated by the combined force of Kanao and Inosuke, avenging Shinobu and her family.
While he reflects on his motivations, Gyomei is able to crush his head with his flail, again beheading Kokushibo. The Upper Rank attempts to regenerate, but to his disbelief, his flesh begins to crumble away and he is rendered unable to use his Blood Demon Art as a result of Muichiro's red blade stuck in his body.
However, unlike many other characters, Nezuko will not die at the end of the series, but will revert to her human form during the Final Battle arc.
Upper-Rank Two: Doma
Kanao Tsuyuri and Inosuke then teamed up to fight, but were no match for him until the 37 kilograms of Wisteria poison he'd inadvertently ingested by consuming Shinobu began to melt his body.
The Upper Moon Five has a record of killing 15 Hashira in the past, solidifying his position in the Twelve Kizuki.
The remaining slayers began landing blow on him as well, ending with Gyomei and Sanemi beheading him. However, much to their horror, Kokushibou's head regenerated and turned into a much more monstrous form.
The Water Hashira, Giyu, survived the "Infinity Castle" arc after fighting beside Tanjiro against Akaza and Muzan.
Doma is always smiling and acts very friendly, but this cheerful, caring nature is simply a facade. He states that he cares for his fellow Upper Moons and even cries when he learns that Akaza died, though, in fact, he doesn't feel anything for them.
She was killed by Doma.
Although Inosuke refuses to acknowledge that he has met him before, Doma explores his memories and reveals that he met Inosuke when he was a child, and was responsible for killing his mother, causing Inosuke to fill with hatred and engage in combat with the Demon.
Demon Slayer's season 3's latest episode has left fans on edge with Tanjiro's discovery of Yoriichi Tsugikuni's Type Zero sword.
When Yoriichi moved forward to kill him, Muzan used the remains of whatever power he had left and divided his body in a powerful burst. Though Yoriichi was able to destroy nearly all the fragments, the pieces he missed escaped and allowed Muzan to regenerate again.
Yoriichi was powerful enough to defeat Muzan; however, he couldn't do so. That's because he couldn't come down to kill his twin brother, leading to his own demise. Even to this day, Muzan is scared of Yoriichi.
The warrior Muzan feared was a swordsman named Yoriichi Tsugikuni. Yoriichi was the only slayer before Tanjiro who came close to killing Muzan, and the flashback of their fight occurred in Chapter 187.
Thanks to Somiyoshi, and later on Tanjuro who passed it down to Tanjiro, the world is left with a weapon to defeat Muzan Kibutsuji, long after Yoriichi passed away. Those are ultimately the role of Tanjiro's father, Tanjuro Kamado, in the story of the Demon Slayer.
Tanjiro Kamado is the only (known) living user of the Hinokami Kagura, but unlike the Water-Breathing he was taught by former Hashira Sakonji Urokodaki, Tanjiro learned Sun-Breathing from his and Nezuko's late father, Tanjuro Kamado.