I would think you have to be a full-time student as well. A lot of Exchange programs are done by paying full-time tuition to your home university of your own country. If you give it some time and become a full-time student, when your in-stat rates kick in you shouldn't have a problem. Just make sure your school has an exchange program in Japan. My university in Pennsylvania has an exchange with Kansai Gaidai, as do many other schools thoughout the US.