Senjuro Rengoku

Senjuro is a pale boy with thick black eyebrows above large golden eyes that turn red near their white pupils, angled to give him a soft yet steady look. He strongly resembles his father and brother, his unruly golden hair spreading around his face with red-tinged ends and tied loosely at the back. He commonly wears a plain white robe and underlayer paired with darker hakama secured by a red sash.

First shown mourning his brother and beaten down by his father's verbal cruelty, his real character emerges when he talks with Tanjiro: kind, caring, and quick to find the bright side of things. He keeps hope for his own future and believes Kyojuro would forgive him for ending the family's unbroken line of Flame Hashira.

Following the fights with Enmu and Akaza, a wounded Tanjiro arrives at the Rengoku household to pass on Kyojuro's last words. Senjuro is already aware of his brother's death and instead gently asks how Tanjiro is doing. Their father Shinjuro then bursts in, flinging vicious insults at Kyojuro for ever having joined the slayers, which leaves Senjuro in tears. Tanjiro speaks up for the brothers, and the argument escalates into a short scuffle with the former Hashira.

Afterward, over tea, Senjuro thanks Tanjiro for confronting the father he himself was too afraid to challenge. He retrieves a chronicle of the Flame Hashira for Tanjiro, only for the two to discover that Shinjuro had ripped it apart, and as a parting gift he gives Tanjiro the tsuba from his late brother's sword.

Though he comes from a long line of Flame Hashira, Senjuro never developed the ability to make his blade change color and abandoned the way of the sword. He decides instead to recover the lost chronicle through other means and to write to Tanjiro should he learn anything, starting a lasting exchange of letters between them.

During the battle with Akaza, his letter describing a hidden thirteenth Sun Breathing form reaches Tanjiro after the fight. Once Muzan has been defeated, Senjuro calls on the recovering Tanjiro together with a far calmer, reconciled Shinjuro, and his line is later said to carry on through his descendant Tojuro, who looks much like the late Kyojuro.