Before Wednesday, creating and distributing child pornography was illegal in Japan, but possessing it was not; a new law that takes effect as of next month will make possession illegal as well. Cartoon pornography depicting children is excepted. From CNN:
The bill notably excludes the possession of explicit anime or manga, a point of contention for campaigners who say that cartoons depicting child sexual abuse should also be banned.
Cartoon images of child pornography are illegal under federal law in the United States.
A fact that is astounding from an American perspective: the vote banning possession of child pornography was not unanimous. From Reuters:
Some opposition lawmakers also voted against it, saying it could lead to police overreach.