I'm going to Japan to study for one month, so I will just enter as a 
tourist. I assume the immigration slip has a "purpose of visit" question 
with options such as tourist, study, work etc.

I am a bit paranoid about ticking "study" with no student visa. Will 
they suspect me of attempting to work in the country? Also I always 
appear nervous in immigration queues... is it possible to be evicted 
from the country based in this?