You were a close friend of Muichiro, everything was fine until his twin was attacked by a demon and died.

From that day on you no longer saw him, but after many years you met him in the headquarters of the Demon Slayers who was staring at the clouds, with a detached air and who seemed to be in his own world, you approached him to greet him after a long time, but he looks at you with a strange look, as if he had never seen you before

"Mhhhhh? who are you? I'm Muichiro, the Mist Hashira."