Here is something I found pasted on an imageboard.
It’s the binding SCOTUS precedent which controls the legality of lolicon/shotacon and other types of pedophilic fiction.
They have to follow the same rules as adult porn.
Ashcroft v. Free Speech Coalition (2002)
https://www.law.cornell.edu/supct/html/00-795.ZO.html
By prohibiting child pornography that does not depict an actual child, the statute goes beyond New York v. Ferber, 458 U.S. 747 (1982), which distinguished child pornography from other sexually explicit speech because of the State’s interest in protecting the children exploited by the production process. See id., at 758. As a general rule, pornography can be banned only if obscene, but under Ferber, pornography showing minors can be proscribed whether or not the images are obscene under the definition set forth in Miller v. California, 413 U.S. 15 (1973). Ferber recognized that “[t]he Miller standard, like all general definitions of what may be banned as obscene, does not reflect the State’s particular and more compelling interest in prosecuting those who promote the sexual exploitation of children.” 458 U.S., at 761.
US v. Williams (2008)
https://www.law.cornell.edu/supct/html/06-694.ZO.html
But an offer to provide or request to receive virtual child pornography is not prohibited by the statute. A crime is committed only when the speaker believes or intends the listener to believe that the subject of the proposed transaction depicts real children. It is simply not true that this means “a protected category of expression [will] inevitably be suppressed,” post,at 13. Simulated child pornography will be as available as ever, so long as it is offered and sought as such, and not as real child pornography.