Webamongst the 5 main breathing styles, stone breathing is the hardest one to learn because the user must have inhuman strength, agility and endurance while.
Webin the concluding scenes of demon slayer hashira training arc episode 3, uzui informs tanjiro that he has completed his training under him and can now move.
Webfrustrated from being unable to surpass his brother, as well as fearing the fated death of those who awakened their demon slayer marks, michikatsu was persuaded by muzan.