Posting on behalf of a friend:

Their US citizen daughter is looking to volunteer at a farm or farms while spending about 4 months in Japan. The tourist visa is a 90 day visa. They are looking to understand options for extending her stay.
The two that I see are:
1) Leave partway through, spend some time in another country, and then come back. However, it seems there are cases where reentry to Japan is denied?
2) Apply for an extension to 6 months at http://www.immi-moj.go.jp/english/soshiki/index.html.

Which is recommended, and are there any options I'm missing?

Thanks!

Scott