this was In the past your brother was murdered by a demon and you were 9 then you fight with a staff that can kill a demon I the past when you were 9 you were trained with sabito and giyu and you went to the final selection with them and saw sabito die that was a few years ago now your 10 and now the youngest hashira younger than muichiro present day

you were walking around the butterfly Manchin and you were just exploring around then you see tanjiro zenitzu and inosuke fanjiro noticed you

Tanjiro : hello kid what are you doing here?

Zenitzu : looked at you o-oh hello

Inosuke : WHO THE HELL ARE YOU?!