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TheDemon Slayerseries revolves around themes such as strength, surpassing limits, and perfecting techniques, but to further improve these attributes, a Demon Slayer Corp member needs to go through a training regiment known as the Hashira training.
The Hashira training is conducted by the Demon Slayer Corps and the lower-ranking Demon Slayers are expected to take part in the training to ensure they are physically and mentally prepared for the war against Muzan and his demons. The lower-ranking Demon Slayers go through grueling exercises to ensure their bodies are strong enough to keep up with the demons and are ready for the final battle.

This Is The Way Of Becoming Stronger
Who Are The Hashira? And What Does It Take To Become One?
The term “Hashira” refers to the highest rank in the Demon Slayer corps, and it translates to “pillar” in Japanese. The reason as to why the training is named after the word Hashira is because it is specifically designed to increase the potential of lower-ranking Demon Slayers into future Hashiras. Hashiras are also recognized as the most powerful individuals in the series and they all report to the leader of the Demon Slayer Corps - Kagaya Ubuyashiki.After the death of Kagaya, his son Kiriya Ubuyashiki led the Demon Slayer Corps. The uniqueness of each Hashira is that they each have their own breathing style which they created themselves and perfected.
There are two ways in order to become a Hashira; the first way is that a Demon Slayer would need to kill at least fifty demons or defeat an upper moon demon on their own. The second way is to become a disciple of a current Hashira. The only way the disciple can become a Hashira then is if the respective Hashira dies or retires. Becoming a Hashira takes almost five years of dedication and hard work, but the more talented a Demon Slayer is, the quicker they become a Hashira. Muichiro Tokito, the current Mist Hashira, managed to rise through the ranks after two months of being in the Demon Slayer Corps. There are also scenarios where a designatedsuccessor is given to a Hashira. A Demon Slayer can also choose to apply for the position or get selected by the Hashira themselves.

The Stages Of The Hashira Training, Explained
The Obstacles The Demon Slayers Need To Go Through Are Intense
The Hashira training consists of various stages of training modules that Demon Slayer Corp members need to go through, and a Hashira overlooks each stage. For the fitness and stamina training, the former Sound Hashira, Tengen Uzui ensures that all Demon Slayers possess the necessary stamina and physical fitness needed, by making them run continuously for long periods of time until exhaustion. The rapid movement training is conducted by the Mist Hashira, Muichiro Tokoito. This training enhances the body coordination of a Demon Slayer as they spar against Muichiro.
Flexibility training isconducted by the Love Hashira, Mitsuri Kanroji, where she trains the Demon Slayers, to dance to music and is then put through painful and rigorous stretching. Next up is sword skill training where the Serpent Hashira, Obanai Iguro gets the Demon Slayers to spar against him.

The Wind Hashira, Sanemi Shinazugawa also puts the trainees through an infinite striking training process where the Demon Slayers are attacked until the point they faint. In order for their bodies to become even stronger, they finally go through muscle amplification training with none otherthan the Stone Hashira, Gyomei Himejima where they need to be able to stand under a heavy waterfall for long periods of time, carry heavy logs of wood on their shoulders and lastly use all their concentration and power to push a larger boulder. The Hashira training is not just beneficial for the Demon Slayers in training, but also for the Hashira to improve their skills and unlock the Demon Slayer mark.