Unless it's from the same developer, someone else couldn't take those characters and make their own game.
That wouldn't be a problem, really, but I guess that you are talking about the legal aspects.
In this case I gotta say, that is not what people care the most about here - if you look at any game page, I am sure you will find at least ten parody games and those are characters that would end people's lives if the owners' lawyers came after these small time developers.
That said, I kind of doubt that ICSTOR has paid for all the assets they use.
But really, if we want people here to stop breaking the law, I think under!age shit is the first that would have to go. That stuff will definitely be able to close the entire site down and there are hundreds of games that violate the legal "minimum obvoiusly visual age of 18" rule because the operators of f95 think that their own rule 7 actually is the one that applies.
