As everyone knows, Japanese society has this complicated relationship with tattooing. In Japan, being inked has been for a long time, and still is for many people, a sign of belonging to yakuza, the local mafia. However this (slowly) tends to evolve, for example in small neighborhood sento (communal bath house) where tattooed travelers are easily accepted. It must be said that young Japanese people have more and more fashion tattoos as modest designs occasionally visible.
As foreigners, there is a higher probability for tolerance if your tattoo is just a bit seen, for example on your leg or arm. Hard to imagine a yakuza gang member with no slanted eyes, carrying a backpack with a camera. If your ink is covered beneath clothing, we strongly recommend you to mention it at the front desk of an onsen or any public pool or hot spring water park, and then to respect the establishment settlement in case of a bathing ban.
Japanese people, on the other hand, have to be more rigorous especially in their workplace. It is officially the case at the Osaka city government since 2012 when Toru Hashimoto, the mayor at the time, started to ask to its 38,000 employees to voluntarily report any tattoos on their body. Indeed, a few months earlier, one of them showed off its inkwork to a child at a welfare center, causing a light complain.
Each government worker must fill out a nominative document (see below via), mentionning whether or not (s)he has a tattoo and if so, on which part of the body, its size and for how long. Body parts concerned are: arms (from shoulders to fingers), legs (from knees to feet), as well as neck and head.
The Osaka city legal department confirms that this survey does not interfere with the law or human rights to privacy. The document’s instructions clearly say that "it is not appropriate [for a public servant] to work in outfits revealing your tattoos" and the provided details will be first treated during personal interviews with employees.
Still in Osaka, another tattoo case that started in 2015 is Taiki Masuda's trial, a Japanese tattooist who was sued for operating three women between July 2014 and March 2015 without a medical license. After being fined ¥300,000 (~US$ 2,788.10), he appealed a first time which lowered his fine by half. Finally the High Court of justice completely acquitted him in November 2018, ruling that his process is not a medical practice. Masuda took advantage of this media coverage to co-found an NGO called "Save Tattooing in Japan" that remains active today.
Little by little, the society is trying to forget the traditional symbolism of tattooing to turn it to a more artistic and only design meaning. There is still some way to go so that the Japanese people can be inked without being cataloged to the yakusa cast. For foreign travelers, the pressure is certainly less strong but ban policies (if there have any) must be respected.
A final topic about Japanese language: do not confuse タトゥー tatoo, ink body tattooing, with 落書き rakugaki, street art and graffiti.