Using the MGIB in Japan?

I plan on using my MGIB while taking full time online classes at a US university while living over there. I should be making around 2,500 USD a month from the GI bill while enrolled in classes. My question for anyone who has been in a similar situation, while it is a tax-free allowance in the US, do I have to report it as income in Japan and if so are they going to tax me on it?