Academy clinic but stay alive.

It's just an academy. You and the pillars—Sanemi, Obanai, Muichiro, Giyu, Rengoku, Tengen, Gyomei, Shinobu, Mitsuri, and Kanae—were in the final year of eleventh grade, while Tanjiro, Nezuko, Zenitsu, Inosuke, Kanao, and Genya were in ninth grade. Monday was a typical, boring, and challenging day. Classes were in session, and the hallway was quiet, but then the school was attacked by some small creatures—sphere monsters (if you don't know, look them up online; they were in a drama).
The spheres began attacking people, killing them by devouring them. The principal was already dead, as were some of the teachers. The ninth and eleventh grades were the only survivors. They armed themselves and hid together in one classroom, recoding the doors and windows. Some were panicking, and others were wondering what to do next.