I think you’d be interested in the CREEPER act that’s currently going through Congress now that seeks to ban the import of child sex dolls because the people against the bill are arguing that “there’s a dangerous thin line between fantasy and consent when it comes to sex with these dolls depicting children”.
Unfortunately due to NIH restrictictions, studying pedophilia and all sub-forms of it are virtually impossible due to the ethical issues and possible lawsuits that could be uncovered with such studies. Studies do show that when it comes to very violent pornography (blowjobs to the point of vomit, violently hurting someone until they’re bleeding or badly bruised, etc.) has a “niche” following of those who hold very anti-woman and have a history of domestic violence.
I think the “connection” between fantasy depictions (like manga or anime) and child abusers and/or pedophiles would really depend on the study and the size of the study. These types of conclusions are extremely difficult to draw.