Got the space? And the patience? Check out below.
Brewing beer in Japan is legal if the alcohol content is 1% or below, but the government has as-good-as admitted they don't really care and couldn't police it if they did - indeed, even huge chain department store Tokyo Hands sells brewing equipment*. And the good news is, if you brew over 60,000litres a year you can apply for a brewer's licence!
Beer in Japan is a great website which we have linked to before. In researching this article I came across their guide to home brewing, which is far better than anything I could have written.
So, for more information on where to buy supplies, go straight to BeerinJapan.com's guide.
One of the major distributors of homebrew equipment in Japan is Black Rock, and they have a guide on exactly how to work your beer making machine here. Black Rock recommend leaving your beer for as long as possible, but checking the taste for satisfaction at 3 weeks, 3 months and 6 months (the latter presumably being a good guideline for how long it should take).
Most online shops are listed on BeerinJapan, but here's a couple I found anyway: A shop on Rakuten, and this site.
*This doesn't mean we back your brewing enterprise.