Muzan was responsible for killing many humans and Mitsuri was one of them.
Hopefully, there aren't any anime-only fans reading this entry, as Mitsuri Kanroji only just appeared in the anime again, but yes, she does tragically die alongside most of the other Pillars.
1 Mitsuri & Obanai
It was obvious for most of the series that Obanai and Mitsuri were in love, but they never confessed until they were dying by each others' side after the final battle against Muzan.
Mitsuri Kanroji, the Love Hashira, participated in the final battle against Muzan Kibutsuji and perished, alongside her friends Gyōmei Himejima, the Stone Hashira, and Obanai Iguro, the Serpent Hashira.
Mitsuri swiftly defeats a fish demon with First Form: Shivers of First Love.
Suddenly, Mitsuri Kanroji grabs Muzan's left arm and rips it clean off his body in anger sacrificing her own arms in the process. Sanemi Shinazugawa appears and quickly chops off Muzan's right arm as well with the Wind Breathing, Eighth Form: Primary Gale Slash.
Shinobu Kocho is a capable Demon Slayer whose worthy of being the Insect Hashira. That being said, she's arguably the weakest Hashira when it comes to pure strength.
In Chapter 205, we see Obanai and Mitsuri reincarnated and married, as they promised before they died, and they are running a restaurant together. In the volume extras it is revealed that they have five kids.
Tomioka Giyu = killed by Tanjiro Kamado. Tanjiro Kamado = killed by Nezuko kamado ( or another demon ) ; or executed for killing a hashira and have protected a demon. Nezuko Kamado = burned to sunlight , killed by a hashira , or eaten by Muzan Kibutsuji ( if she conquires the sun )
Something I noticed with Iguro and Mitsuri is that in the final battle Iguro loses his eyes and Mitsuri loses her arms which Iguro's heterochromia and Mitsuri's freakish strength are major causes for their respective tragedies and even though Mitsuri cannot hold him and Iguro cannot see her they proclaim their love for ...
The Wind Hashira has one of the saddest backstories in Demon Slayer. His mother had turned into a demon and had killed five of his siblings. He was forced to kill his own mother in an attempt to save his only remaining brother, Genya.
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.
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.
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.
Demon Slayer: Kimetsu no Yaiba's Mitsuri Kanroji is another Hashira who effectively established their strength level in their proper introduction. In the “Swordsmith Village” arc, Mitsuri held her own against the Upper Rank 4 Kizuki, Hantengu, and while she needed help to win, it was still nonetheless impressive.
Mitsuri is a voluptuous young woman with a kind face. She has pale green eyes with small moles under each eye. Her most defining feature would be her long hair usually tied in three braids which is pink and fades into neon green halfway through.
Who is Rengoku girlfriend? Mitsuri Kanroji. The two of them share a gluttonous side and enjoyed snacking on their breaks. Mitsuri derived her own unique Breathing Style, Love Breathing, from his Flame Breathing.
Later it is revealed that he married fellow slayer Kanao Tsuyuri. In the Modern World, Tanjiro and Kanao had descendants named Sumihiko Kamado and Kanata Kamado.
Towards the final arcs of the manga, Tanjiro is mortally wounded and dies during a fight with the Demon King Muzan. Though Muzan is also seriously injured, he uses the last of his powers to turn Tanjiro into a demon.
As for the "last ever Hashira"...that would be Shinazugawa-san as well as Tomioka-san.
9 The Insect Hashira - Shinobu Kocho
Kocho follows in the footsteps of her older sister Kanae Kocho, who was a Hashira before her death, several years prior to the timeline of the anime. Shinobu Kocho is Demon Slayer's only known Insect Breathing practitioner.
But there is one who is the friendliest of them all, and that is Kiyogiro Rangoku, the Flame Hashira. Among the pillars, there is not a single negative thing revolving Rangoku. Such an honest guy, and his character influences others positively. In Demon Slayer, Liu and Rangoku are not shown to have any interactions.
Tengen Uzui
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.
Gyomei Himejima is the strongest Hashira in Demon Slayer. This fact has been established in the manga as Tanjiro, Inosuke and Zenitsu all agree that he is the strongest member of the Demon Slayer Corps. His strength was showcased during the fight against Kokushibo.