It'll happen eventually, I don't know why people seem to think that japan is immune. If you look back to how the western world looked before this shit took root it was pretty easy to say "this kind of stuff will never work here", hell people were still saying that about whatever little corner of the world they had (such as STEM, The US South whatever). It's already started if you know where to look, there's universities in japan that have courses like :
"African Americans, Equality and the Law: Weapon or Tool?",
"Politics of Identity in America "
"Special Topics in Asian Studies I: Social Inequality in Asia"
"Japan in a Changing World Order S"
A university recently replaced its beauty contest with basically a social justice contest(Who had the best cause, was most "interesting" and such), reasons the students who campaigned for this cited were that it separated masculinity and femininity, promoted lookism, objectified women ect. Not to mention the BLM protests that were held there recently. Yes, it's happening only in certain areas, usually the ones with some foreign pop or at least foreign ties but that's how this stuff starts.
This "japan is immune, they're different!" stuff is a huge cope and is basically helping this shit out. You'll have the same cycle but faster there and people will be saying "It's not SJW, it's normal, it's always been this way, it's human rights" until it goes far enough that they don't have to.
The Japanese people are less inclined to speak out and more conformist, if anything there will be less people willing to speak out. It'll be a Japanese strain of PC for sure, but it will be the same in all the important ways.
Anime is a huge industry in japan and a good export of their culture, it will definitely be one of the first places they'll get at. There was already a surprisingly woke anime movie, called something like Japan underwater 2020 or something. If you want to see how it will happen just look at what happened to comics/games/movies and imagine it faster and quieter. As for how soon? Until they get as bad as the western industry is? 15-20 years maybe, not sure.
I personally can't wait for the first shaniqua-san.