I have a tattoo (now two, but only one when I was in Japan), and I was allowed to go into the onsen. My tattoo was rather visible too. Most Japanese people found it interesting or cute. One shop attendant told me "Sono tattoo ha kawaii desu ne" and when I was in line at the grocery store, and ojisan talked to me and show me the tattoos he had on his legs. :) So I really had no problem, and I'm not heavily tattooed at all though. You can work it you tattoos as long as they are not overtly visible and easily hidden (i.e. you wouldn't want to be having full sleeves, neck tattoos, face tattoos etc.). I did see a yankii looking guy that was fully tatted up though. He had blonde hair and looked kind of dangerous though lol. I honestly feel like tattoos are very slowly becoming more acceptable. Not mainstream, but there are even come celebrities that have them. I know a couple of guys in EXILE have them.
