Tsuguko

The Tsuguko serves as a reserve candidate for the Hashira ranks within the Demon Slayer Corps. Only a handful of warriors ever earn the title, and each must first impress a sitting Hashira. Mastery of one of the Breathing Styles is treated as a basic requirement. A Tsuguko often studies the same style as their mentor, though that is not mandatory. Kanao Tsuyuri, for instance, trains under the Insect Hashira Shinobu Kocho yet practices Flower Breathing, the style from which Insect Breathing originally branched.

The word can also be used loosely as praise. Tengen Uzui, the Sound Hashira, calls Tanjiro Kamado, Inosuke Hashibira, and Zenitsu Agatsuma his Tsuguko even though none are formally his students.

There are two paths to the position. One is application, in which a slayer requests the role and is accepted. Genya Shinazugawa pursued this route, eagerly seeking to apprentice under the Stone Hashira Gyomei Himejima despite being unable to use a Breathing Style. Gyomei declined to name him a Tsuguko but still trained and guided him. The other path is scouting, as when the Flame Hashira Kyojuro Rengoku personally invited Tanjiro to join him after recognizing his promise.

The main purpose of a Tsuguko is to take over should their Hashira die or retire. If the apprentice uses a different Breathing Style, they may rise as a Hashira in that style instead, keeping the Corps strong across generations. Such apprentices are scarce because many recruits are intimidated by a Hashira's raw power or worn down by the punishing training.

Kanao Tsuyuri is the best known Tsuguko, serving under Shinobu Kocho. Shinobu actually had three other apprentices before Kanao, but demons killed them, giving her the largest recorded count at four. Kanao is regarded as the final Tsuguko in the entire history of the Corps.

Mitsuri Kanroji trained under Kyojuro Rengoku, though her status as his Tsuguko was only confirmed later through the Taisho Secret in Episode 63. With the Demon Slayer Corps dissolved following the defeat of Muzan Kibutsuji, the position passed out of existence entirely.