Tengen Uzui/Synopsis

History
Tengen was one of nine children from a surviving line of shinobi. However, seven of his siblings died by the time he was 15, leaving only him and the second-youngest brother. The harsh, abusive training their father made them endure made his brother become just like their father: uncaring towards life and using people as tools.

Disgusted by this worldview, Tengen chose to rebel with the values that were instilled in him during his youth. He instructed his wives to value their own lives first, innocent civilians second, and his own last, even though it completely defied their training.

Some time later, they were taken in by Kagaya Ubuyashiki and Tengen joined the Demon Slayers. He became a Hashira some time before Sanemi Shinazugawa, as he was present at Sanemi's first Hashira meeting and expressed annoyance when the new Hashira confronted their leader.

Functional Recovery Training Arc
Tengen was present as a member of the Hashira when Tanjiro Kamado was put on trial. Upon initially meeting Nezuko and Tanjiro, he openly expresses his distaste at the idea of them travelling together, even claiming that he will "cut off (Tanjiro's) head with style."

When Tanjiro explains his reasoning for travelling with a Demon, the Sound Hashira becomes intrigued and even requests to see their interaction. However when the leader of the Demon Slayer Corps informs the Hashira of his acceptance of the siblings, Tengen openly rejects the idea of allowing Tanjiro to remain with Nezuko.

Demon Train Arc
Although Tengen did not participate in any major battles during the arc, he receives news of Kyojuro's death from a Kasugaigarasu. He expresses his concern that even Kyojuro had lost his life to one of the Upper Rank Moons.

Entertainment District Arc
Tengen enters the arc by kidnapping several girls from the Butterfly Estate to assist him on his mission. Tanjiro, Zenitsu and Inosuke confronts him and volunteers to go on the mission in the girls' stead. The Sound Hashira agrees and reveals that his mission is to investigate the Red Light District and re-establish contact with his three wives that he sent in to spy on the location, but had recently lost contact with. After having the three boys cross-dress as girls and selling them to individual brothels, Tengen Uzui plays a more background role for a few chapters as the boys gather information on the possible demon lurking within the district. After it's revealed that most of his wives had been captured and missing, he immediately goes to rescue the nearest one, therefore not being present to aid Tanjiro in his fight against Upper Moon Six, Daki. Tengen arrives back on the scene just in time to apparently finish off Daki with a single attack, but this is quickly proven false when Daki reveals she cannot be killed because of her Demon blood connection to her brother, Gyutaro, the true Upper Moon Six. In the fierce ensuing battle, Uzui is immediately weakened by Gyutaro's poison, and by the end of the fight had lost a hand. As he lay dying from the poison, he lamented on his inability to say some flamboyant last words, until he was saved by the timely intervention of Nezuko Kamado using her Blood Demon Art to burn the poison out of his system. After this, Tengen informs the freshly arrived Serpent Hashira, Obanai Iguro that he's officially retiring from the Demon Slayer Corps.

Hashira Training Arc
Despite officially retiring, Tengen assists in Hashira Training along with his wives. He oversees the first level, which is basic stamina training.

Dimensional Infinity Fortress Arc
Tengen and Shinjuro Rengoku were located in another section of the Ubuyashiki estate when it was taken into Muzan Kibutsuji's Dimensional Infinity Fortress. They stand guard outside of the room Kiriya, Kanata, and Kuina Ubuyashiki are located in as the surviving Ubuyashikis map out the fortress and give instructions to the Demon Slayers.