My take on this is part fan rant, part practical breakdown: websites treat 'JoJo's Bizarre Adventure' adult fan art the same way they treat any other explicit fandom content, but with special attention to character age, copyright, and community norms.
At the platform level you'll see a three-layer approach. First, there's policy: a site's terms will define what's allowed (explicit content allowed in age-restricted areas, entirely banned, or tolerated with strict tagging). Second, automated systems scan uploads for nudity or sexual imagery using NSFW classifiers and image hashing systems; these either block content outright or queue it for human review. Third, human moderators and community reports handle nuance — ambiguous poses, fan-interpretation vs. original depiction, or contested cases where a character might look underage. Legal obligations (CSAM zero-tolerance, DMCA takedowns for copyrighted material) force fast removals in some cases.
Community culture matters too. Artist-friendly platforms often provide explicit tagging/age gates and private communities; mainstream social networks push artists toward paywalled or clearly
marked sections or disallow explicit fan content. For creators who want to stay safe, clear tagging, avoiding younger-looking characters, and using platforms that explicitly allow R18 work are practical moves. I still love seeing bold fan art, but I get why sites have to be strict — it's a messy balance between expression and safety, and I pick platforms more carefully now.