Fortunately, Zenitsu was able to single handedly beat the Upper Moon 6. Not only did he defeat the demon, he also created a seventh form called the Flaming Thunder God. These are the demons who have been given the title of Upper Moon 6 in Demon Slayer.
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.
However, against all odds, Tanjiro along with the rest of his crew were able to defeat the Upper Moon 6. This was also the first time he activated his Demon Slayer Mark as well. Fans absolutely loved this fight in the Entertainment District arc.
After becoming a Demon Daki grew strong enough to kill and eat seven Pillars and gained the attention of Muzan Kibutsuji who allowed them to join the Twelve Demon Moons. She later dies after being beheaded by Zenitsu Agatsuma and Inosuke Hashibira.
As a demon, Kaigaku had eaten many people and became powerful enough to become the new Upper Rank Six of the Twelve Kizuki by the start of the Infinity Castle Arc.
Daki (Upper Rank Six, formerly)
Tanjiro only managed to slice off Gyutaro's head when he "summoned a hundred times" the strength in his body, which awakened his Demon Slayer Mark in the process, to successfully cut through his neck.
Nezuko setting Tengen on fire. By the end of the battle, Gyutaro's poison has spread throughout Tengen's body resulting in his inability to speak. As he lays dying from the poison, Nezuko Kamado intervenes and uses her her Blood Demon Art to burn the poison out of his system, allowing him to rejoice with his wives.
Demon Life
At some point, Daki fought, killed and ate seven Hashira. Two days before Tanjiro Kamado and company infiltrated the Entertainment District, Daki was confronted by Omitsu, the manager of the Kyogoku House, over her mistreatment of the staff.
We first see Doma when he is still the Upper Moon Six while he is in the middle of eating a geisha. Later he becomes even stronger and rises to the position of Upper Moon Two. He dies because of the lethal amount of poison he absorbed through Shinobu Kocho's body followed by Kanao Tsuyuri beheading him.
Given how talented Tanjiro is, it's likely he'd defeat Zenitsu, even if the latter could fall asleep and call on his powers. Tanjiro's demonstrated his ability to take down more powerful demons and adapt to training on more than one occasion, so it just makes sense.
Uzui decides to save Tanjiro and Hinatsuru, throwing himself and Gyutaro off the roof and away from the two.
Nezuko is undoubtedly a strong demon in Demon Slayer and she proved her strength repeatedly. One situation that really displayed her true potential was the fight against Daki. She underwent a transformation and thoroughly overwhelmed the Upper Moon 6 demon.
Doma (in Japanese: 童磨, Dōma) also spelt Douma, is a major antagonist in the manga/anime series Demon Slayer: Kimetsu no Yaiba. He is a powerful Demon under Muzan Kibutsuji as Upper Rank Two (formerly Upper Rank Six) of the Twelve Kizuki.
Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that compliments his position as Upper Rank One.
Kotoha Hashibira
As a result, Doma killed her pursuers, and accepted Kotoha and her baby into his temple. Doma grew fond of her due to her beauty and singing ability, intending to keep her alive until she died of natural causes.
Muzan Kibutsuji
Muzan himself never thought highly of Daki and didn't reciprocate her devotion whatsoever, only ever talking to her to sweetly manipulate her into defeating Demon Slayers on his behalf.
As a member of the Upper-Rank Six, Daki was extremely powerful. She was much more powerful than the regular demons. Her physical abilities were on a completely different level in comparison to some demons that Tanjiro and co. had faced. Daki was immune to decapitation when her brother was attached to her core.
Sound Hashira
He is the fastest Hashira, and the second physically strongest. Obviously, then, Tengen Uzui is rather proud. He is demanding, fussy, boastful, and prone to selfishness. But he is also ultimately kind and caring, with great love for his three wives as well as the other Hashira.
However, Uzui loses one of his arms and an eye in the fight, leaving Tengen Uzui with no choice but to retire from the Demon Slayer Corps. Also, the manga never specifies how the sound Hashira Tengen Uzui dies in the future, which gets us to the conclusion that he passes away from a natural cause.
1/14 He Has A Descendant
Like most of the characters, Tengen Uzui does have a descendant that looks just like him. His descendant is named Tenma Uzui and he's an Olympic-level gymnast representing Japan.
Tanjiro decapitates Akaza with the Hinokami Kagura: Setting Sun Transformation. Akaza was bewildered, wondering how Tanjiro did not have any fighting spirit, comparing this feeling to fighting against a plant. He acknowledges that Tanjiro surpassed his speed.
Tengen lost his arm and was seen lying on the ground unconsciously because of the effect of Gyutaro's poison. Subsequently, he rejoined the battle by protecting Tanjiro with one blade in his right hand and the other clenched in his mouth.
Over a century ago, Doma held the position of Upper Rank Six ( 上 じょう 弦 げん の 陸 ろく , Jōgen no Roku?), and during that tenure, he turned Gyutaro and Daki into demons and introduced them into the Twelve Kizuki.