Tengen Uzui/Synopsis

History
Tengen was born into a family of nine children within a shinobi clan. Three of the nine children died before they even reached 10 years old due to overzealous training. With the remaining six of his siblings, they were forced to kill each other on their father’s orders without them knowing who they fought, as their heads and faces were covered with masks. Tengen realized his father's trick only after he had killed two of his brothers. By the age of 15, seven of his siblings had already died leaving only him and his younger brother who is two years younger. As children, his father had forced them to undergo harsh and intensive training as an attempt to save the clan, and influenced them to believe that they needed to dispose innocent lives for their benefit, and solely have a wife as means for producing offspring. As his last remaining brother adopted this mindset, and did not feel bad about killing their other siblings, Tengen became appalled and decided to leave the clan permanently. He left the village with his wives without fighting his brother.

The Uzui family practices polygyny, so when Tengen turned 15, he must have 3 wives, who were chosen by the head of the clan. After leaving the village with his wives, he would later teach them to value themselves before the mission, going against their teachings as kunoichi. For a while after he had left the clan, it became habit for him to say he was going to hell, but he stopped after Makio got angry with him, Hinatsuru cried, and Suma bit him. He anguished over whether he should have exterminated the Uzui clan, but he couldn't bring himself to kill his father or brother. Following the departure from his clan, Tengen and his family searched for Kagaya Ubuyashiki to help fight for the Demon Slayers, and he formally joined. Tengen would later go on to climb the ranks of the Corps and become the Sound Hashira before Sanemi Shinazugawa became a Hashira, and when Kanae Kocho was a member.Notably, Kagaya empathized with Tengen and could only imagine how difficult it had to have been for him to abandon everything about his past to take on a new path and this was this empathy that caused Tengen to become deeply devoted to the Oyakata.

Rehabilitation 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 his 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.

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

Entertainment District Arc
At the beginning of the arc, Tengen enters Butterfly Mansion and attempts to kidnap Naho and Aoi to assist him on his mission. However he is forced to change tactics when the three boys &mdash;Tanjiro, Zenitsu and Inosuke Hashibira&mdash; rescue the girls, and force him to take them along on his mission.

On their way to the site, Tengen reveals that they are going to investigate the disappearance of his wives within the Entertainment District. In order to do so, he explains that each boy will be sent to one of the three brothels: Ogimoto House, Kyogoku House, or Tokito House to try to gather information on their whereabouts. Once they arrive at the district, Tengen disguises the boys as girls ands drops them off at each house to begin their investigation.

Tengen proceeds to lie low as the boys gather information within each house, and monitors for any unusual activity within the district. After Zenitsu goes missing, Tengen senses the immediate danger and tells the other two boys to abandon the mission and let him complete it for their safety. He reaches the Kyogoku House and holds the brothel manager hostage demanding to know where Zenitsu and Hinatsuru had disappeared to. Upon learning that Hinatsuru had been sent to the Kirimise, Tengen presses the manager for more information and he reveals that Warabihime had been causing the disappearances.

When Tengen arrives at the Kirimise, he discovers Hinatsuru had been held prisoner by Daki's obi and defeats it, before tending to his wife. Once he administers medication to her and checks that she's okay, Tengen instructs Hinatsuru to leave the district and run for safety before continuing his search for his other wives and Zenitsu. When he arrives back in the district, Tengen hears the sounds from the underground cavern, and enters it to discover his wives &mdash;Makio and Suma&mdash; inside fighting the obi. After freeing them, the obi manages to escape and Tengen scrambles after it, with Inosuke and Zenitsu trailing behind him.

Tengen on the scene to discover Tanjiro struggling to control his sister, and quickly decapitates Daki unable to believe that she is the Upper Rank they have been searching for. Upon discovering the truth behind Daki and Gyutaro's presence, the Hashira engages in fierce combat with the Demons. Gyutaro manages to poison Tengen during the fight, preventing him from decapitating the Demon. After they finally manage to bring down the Demon siblings, Tengen ends up losing his left hand and eye in the process.

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. Once Obanai arrives to the scene, he tells him that he is officially retiring from the Demon Slayer Corps and assures him that the trainee he "hates so much" has grown strong enough to fill the void his absence will leave, alluding to Tanjiro. As the Kakushi rush in to clean up the scene, Tengen is then supported by his wives as he walks away to begin his retirement.

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.

Infinity Castle Arc
Tengen and Shinjuro Rengoku were located in another section of the Ubuyashiki estate when it was taken into Muzan Kibutsuji's Infinity Castle. 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.