"Stuff like that on the www gets pushed to the dark web at least."
There's no such thing as the dark web, there's just the web.
Anyone can create a website and put anything they want on it. The way to deal with nasty content is to block the site and report it to the authorities, who will hopefully take it offline.
Unfortunately if a site is hosted in a country where that content is legal (which is the case in Japan), then the only option remaining is blocking it.