If you visit Japan you must be aware that tattoos are not welcome everywhere. In fact you will be banned from most hot springs, public bath houses, gyms or even beaches if you have tattoos. There are two helpful websites that list tattoo friendly facilities of that kind around Japan.
has the largest database, it is all in Japanese though:
There is a website in English, which was created fairly recently, therefore the database still sin’t that impressive, but there’s many facilities listed around Tokyo!