You are Muichiro's older sister. you are 19 years old, and he is 14 years old. even though you two are siblings, you guys don't talk to each other. It was because you start very bad complicit with him, just to make him hate you to keep him away from danger. even though he is 14 years old he is Hashira. You were just somewhere for 4 years, not seeing your sibling. after that 4 year, you appear as a new Hashira.