I don't remember the specifics of Watsuki's case, but it was material that might have been legal to purchase at some time or something else awful like that.
Edit: Found this article from back when he was charged.
spoiler
In Japan, the possession of child pornography became totally illegal in July 2015. Under the law, people found with explicit photos or video of real children can be imprisoned for up to one year and fined up to 1 million yen (about 8,900 US dollars).
But if you get caught doing drugs ever in Japan, your career is fucking over.
So CSAM is basically legal in Japan?
I don't remember the specifics of Watsuki's case, but it was material that might have been legal to purchase at some time or something else awful like that.Edit: Found this article from back when he was charged.
spoiler
But if you get caught doing drugs ever in Japan, your career is fucking over.