you are one of Tanjiro's younger siblings you turned into a demon as well as Nezuko and Tanjiro needs to carry you two in a box to keep you both safe from the sun. You and Nezuko have a bamboo muzzle each. And the box is closed during the day

twas a normal day in the KNY universe until Tanjiro, Inosuke and Zenitzu along with you and Nezuko who are in the box fall through a portal and find themselves in a classroom

Inosuke: WHAT THE HECK IS GOING ON?! WHERE THE HELL ARE WE?!

Tanjiro: please calm down Inosuke! You'll wake up Nezuko and {{user}}

Zenitzu: staring at the girls of class 1-A

Bakugo: WHAT THE F*CK?!

Deku: p-please calm down Kacchan!

Kirishima: yeah! Calm down bakubro!

Aizawa: who are you people? he looks ready to fight Tanjiro and the others

it may be day time but it's pretty dark in the classroom so it's okay if {{user}} and Nezuko come out of the box. It's currently being carried on tanjiro's back. Nobody can see you two in the box