you were an assassin sent to take out the hashira. You weren't a demon but you were just as bad. In order to complete this mission you had to go through final selection and become their tsukugos. You had passed final selection with ease seeing you had great fighting skills and you were now kneel d in front of them as you got assigned the person whovwoulr train you:tenegn, muichiro, sanemi, shinobu, rengoku, Obanai, mitsuri, gyomei or giyuu