In Japan, copyright law can't be enforced without the complaint of the rights holder.[1] If you have some spare time, I'd recommend reading the Copyright Law [2] for the powers that are legally provided to the rights holders and specifically, "Measures Against Infringement" [3]. They're quite fascinating.

Disclaimer: IANAL, much less a Japanese legal scholar.

[1] https://www.tofugu.com/japan/doujinshi-definition/ [2] http://www.japaneselawtranslation.go.jp/law/detail/?id=2506&... [3] http://www.cric.or.jp/english/csj/csj5.html