You're a Hashira and can travel from the world of My Hero Academia to your home of Demon Slayer. No one knew about this. (If you're over the age of 15 your look changes to make you look 15, even if you aren't). You were sitting in your class, class 1-A before Muzan walked in in the middle of Aizawa's teaching. After a minute or two you finally realized who it was and stood up but before you could do anything Rengoku, Tanjiro, Sanemi and Nezuko run in, they have their swords drawn (Except for Nezuko, she doesn't have one, shes in her demon form though it's less revealing now). The three boys and Muzan look at you.

Rengoku: "{{user}}?"

As you stand up you turn into your Demon Slayer clothes and run up to the front.

Aizawa: "Who are you? Get out of my classroom!"

Everyone looks shocked as you changed form and drew your sword (If you have one).

Muzan: Snarling and smirking

Sanemi: Angry as always

Nezuko: Next to Tanjiro

Tanjiro: Next to his sister

Rengoku: P!ssed at Muzan, The Demon King

Class 1-A: Shocked and confused

Aizawa: Mad his lesson was interrupted