As such, the anime is now going to introduce a new character, Kaigaku, who will replace Daki and Gyutaro as the new Upper Moon 6.
Upper Rank 6: Gyutaro and Daki
Gyutaro and Daki are the twin demons that jointly hold the position of Upper Rank 6. Gyutaro is the older twin, and Daki is his younger sister. They are both extremely skilled in combat and possess exceptional abilities.
Upper Rank 6: Gyutaro and Daki
These two are now former Upper Rank Demons, but it's worth including them given the impact they had on Demon Slayer season two.
Gyokko (玉壺 Gyokko) is a member of the Twelve Demon Moons and holds the position of Upper Moon Five in the Kimetsu no Yaiba (Demon Slayer) series. Gyokko's appearance is the most demon-like out of the Upper Moons.
Hantengu (半天狗 Hantengu) is one of the Twelve Demon Moons, and held the position of Upper Moon Four before he was killed and replaced by Nakime in the Kimetsu no Yaiba (Demon Slayer) series.
Since Nezuko is from a Sun Breathing lineage she can survive in daylight. After the final battle against Hantengu concludes she can step into daylight and many theories are available about the phenomenon. One of the theories is that her abstinence from consuming human blood is what saved her.
Post-Transformation
Sensing their despair, Doma offered a chance to him and turned both Gyutaro and Daki into demons.
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.
Akaza was also one of Muzan's favorite demons out of all his subordinates. The reason behind this is Akaza's extreme loyalty to his master. The Upper Rank Three demon was always sent away on special missions, something the Upper Rank 1 and 2 were often denied of.
Gyomei Himejima, the Stone Hashira, is the strongest Hashira in the Demon Slayer corps in terms of strength and swordsmanship. He is the only person who uses spiked flails and an axe instead of standard swords to kill demons. Such a weapon takes immense precision and soundness to use without inflicting personal damage.
Upper-Rank Five: Gyokko
As a fellow artist, Gyokko became distracted by Haganezuka's dedication to sword-polishing and opted to hold off on finishing off a wounded Muichiro. Tokito then manifested his Mark and effortlessly decapitated Gyokko with Mist-Breathing, Seventh Form: Obscuring Clouds.
The curse prevents Muzan's name from being spoken aloud, and any who do will meet a horrible demise. One demon, Susamaru, faced this reality when battling Tamayo. Susamaru accidentally shot Muzan's name aloud, attempting to defend his honor with her mind clouded.
Tanjuro Kamado a recurring flashback hero from Demon Slayer : Kimetsu No Yaiba. He was the husband of Kie Kamado, and the father of Tanjiro, Nezuko, Takeo, Hanako, Shigeru, and Rokuta.
After various battles within the Dimensional Infinity Fortress the remaining Upper Moons are killed by the hands of various Demon Slayers. 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.
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.
Nobody replaced Gyokko. We don't really know why, but the Upper Moon Five slot was just never refilled after his death. I'm assuming that Kaigaku was named Upper Moon Six rather than Five because of the fact that he wasn't yet strong enough to move up to that ranking, but that's a good point to raise.
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.
It is revealed that Muzan's true fear of dying and immense desire to live and survive was due to him being born "dead," where his heart would constantly stop in his mother's womb and was assumed stillborn until he fought to breathe before his cremation.
Haruka Shiraishi: Muzan's Daughter.
Kokushibo was the final Upper-Rank to die during Demon Slayer's "Infinity Castle" arc. Muichiro, Genya, Sanemi Shinazugawa and Gyomei Himejima fought together against Kokushibo, though Muichiro and Genya were no match for him and were killed.
The Water Hashira, Giyu, survived the "Infinity Castle" arc after fighting beside Tanjiro against Akaza and Muzan.
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.
Inosuke Hashibira
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.
In a nutshell, Muzan, being the progenitor of demons, is not scared of Doma. However, he is irritated by his inability to decipher Doma's thoughts and feelings, which is the ultimate control he has over all of his creations.
Doma is one of the most ruthless and insanely strong demons under Muzan Kibutsuji. As Upper Moon 2, he proves to be the absolute antithesis of Akaza. Moreover, their contrasting personalities as demons or mannerisms of rising up in the ranks are the major reasons for Akaza's hatred towards Doma.