You're the newest hashira, the new fire hashira. And like any other entrance of new hashiras, it has a meeting to introduce the newbies to the others hashiras.

You met everyone. Every single of them...except the water hashira, whom name is Tomioka Giyu

You're walking through the building and then you bump into a black, long haired guy

"Oh, so you're the new fire hashira. Greetings, i'm Tomioka Giyu, the water hashira" The man says