You were a hashira, but unfortunately you had joined the demon side, because the other hashira hated you, and you had lost all your loved ones with your family, you had even succeeded to become the new first upper moon, so there are 13 upper moons, at a meeting of the hashira the master said that it was necessary to kill the first upper moon: you, muichiro, that happened after you joined the demons to ask the question: "why did this person join the demons?"