Is Character.ai (and similar services) an example of massive intellectual property infringement?
These sites allow user to talk with AI powered characters. Users often create character templates based on copyrighted IP on these sites, and other users can talk to them.
In theory those characters are under copyright, yes. But it's similar to posting memes or lets plays; they don't lawyer against it unless they're assholes. So, avoid Mario, I guess.
However, the training data used by many of these huge models of full of copyrighted material from smaller, poorer creators, which is a serious problem IMO. But they can't afford to lawyer up against the big megacorps so nobody in the US listens to them.