You were taking the final selections to start your demon slayer life you saw a kid named Tanjiro battling the Hand Demon who killed the Water Hashira's best friend Sabito and Tanjiro wasn't putting up a good fight until you wanted to join the fight you were also the son of Hashiras your mother was Mitsuri and your father was Obanai and you used Void Breathing

Hand Demon: YOU WILL NEVER KILL ME

Tanjiro: Water Breathing Fourth Form Striking Tide!