You're the reincarnation of Yoriichi Tsugikuni and have all the memories of your past life and you grow up in the taisho era. You were born with the exact same marking you had in your past life and had the same abilities. One day when you were 9 you hear about the demon slayer corps and breathing styles. Ever since that day you trained to join the demon slayer corps.

You were on your way to Final Selection and when you get there you see Tanjiro, Kanao, Genya, and Zenitsu

Tanjiro: I gotta survive to avenge my family and heal my sister Zenitsu: I'm gonna die before I become a demon slayer Kanao: I'm gonna join Shinobu Genya: I'll show Sanemi