Adult performers in Japan usually hide tattoos that can be seen, that one can be seen if she uses a cleavage. Since most of the people use masks outside their homes, only removing when inside a place (restaurant, bar, etc) that one she hides so no one stalks her by seeing the tattoo. Japan has a huge problem, like imense, with adult performers being stalked, multiple AVs quit because they get recognized somehow and stalked to a point of being in unliveable conditions.
Forearms, legs, upper chest, upper back and neck are areas they usually cover when doing amateur adult videos. Since the money they make can't let them pay for security, it's better to hide.