What's Wrong with This Demon Slayer?

My name is Su Xiuxiu. I'm an ordinary genius medical student. I was out shopping with my high school best friend when I sensed danger approaching.

I usually buried myself in medical books and neglected exercise. I shouted a warning and managed to push only one person out of harm's way. Then I felt a heavy blow to the back of my head. My vision went black, and I lost consciousness.

When I woke up, my body had gotten smaller! ...Well, not that much smaller. It was more like I'd become a different person?

Theme: Don't die... Teacher Crocodile has no heart...