What's with the Bag, Kamiyama-san?

On his very first day of starting high school, Namito Kominato's homeroom teacher has him sit behind a strange girl who wears a paper bag over her head and is always soaking wet with sweat. Her name is Samidare Kamiyama, a extremely shy girl with severe social anxiety. Ultimately, she meets Hinata Arai (the student council president who's kind and helpful, but alarmingly obsessed with her uniform) and Harusame Amano (a girl who only speaks to a cardboard cutout of a magical girl).

Alt official source