Tsuguko

A Tsuguko is an exceptionally talented Demon Slayer who is designated as the apprentice of one of the Hashira.

Overview
The Tsugoku position acts as a wild card for the Hashira position in the Demon Slayer Corps, which can only be obtained by a select few who have impressed the current Hashira. Becoming a Tsuguko to a Hashira can be achieved through two methods:
 * 1) Application: by applying for the position and being accepted. An example of a Demon Slayer using this method is Genya Shinazugawa, who ardently desired to become a Hashira. Despite lacking the ability to use a Breathing Style, Genya persistently sought to be Stone Hashira Gyomei Himejima's Tsuguko, who was the strongest Hashira of the current generation. While Gyomei didn't make him his Tsuguko, he still provided training and guidance to Genya.
 * 2) Scouting: by being scouted by a current Hashira. An example of this method being used is when Flame Hashira Kyojuro Rengoku personally extended an invitation to Tanjiro Kamado to become his Tsuguko, recognizing his potential and skills.

The ability to use a Breathing Style is considered a prerequisite to becoming a Tsuguko. While it is common for a Tsuguko to utilize the same Breathing Style as their mentor, it is not a strict requirement.

The primary role of a Tsuguko is to step into the shoes of the Hashira they serve under, should the Hashira no longer be able to fulfill their duties. This can occur when a Hashira retires or passes away. In the event that the Tsuguko practices a different Breathing Style than their Hashira mentor, they may eventually assume the position of a Hashira within their respective Breathing Style. This ensures the continuity and strength of the Demon Slayer Corps, as the next generation of skilled warriors is prepared to uphold the responsibility.