This is something that has been debated a lot in Japan over the past few years. Up until June of last year, Japan did not have laws regarding the possession of pornography as regulations are made when the need arises, and there was traditionally no need for such regulation. But the suggestive (although not necessarily pornographic) depiction of underage girls has been quite overt in a lot of media, with magazines being a prime example. The domestic awareness of this juvenile sexualization that was already present slowly culminated to a perceived social problem over the past years, and the awareness overseas caused political pressure to be put on Japan to ban possession. Legislation deeming possession of child pornography illegal was finally passed last year.

This is where your question comes into play. When members of the public were still discussing the need for legislative change regarding the possession of child pornography, there was a bit of resistance from the industry that was benefiting from it. For the people lobbying for the protection of the children it was hard enough getting possession of actual child pornography to be banned, but manga and anime depictions were a gray area that complicated the matter. A lot of arguments can be made for allowing it. After all, murder is illegal, yet it is widely depicted in all sorts of media, and the ages of so-called juvenile characters in manga could be anything the artist wants it to be. They could draw a baby and say it is 50 years old. And while this relatively harmless point continued to be contended, real children were being victimized. As it turns out, fantasy was excluded from the ban. It's important to note, though, that even now many kids are made to pose for cameras in a way that could only technically not be referred to as pornographic, often being mislead to believe their swim suit or cosplay pictures are a stepping stone to a career as a so-called idol or actress. Needless to say they are not building the kind of portfolio that is valued outside of the sex industry, and their exploitation is simply for the benefit of the producers and the children's no-good caretakers.

I am no expert, but I expect the issue of drawn child pornography to stay on the back burner for a while now that it has been excluded from the ban. Suffice it to say that the first steps towards a purge have only recently been taken, and Japan still has a ways to go if it wants to protect real children, let alone figuring out how to tackle the gray area of fiction.