Well I found this of must interest so here is me quoting it.

It is not uncommon in Japan for dedicated fan communities to build on the game world–extending or tweaking the mechanics of popular games.  Sometimes these fans even produce doujinshi–books and fanzines that contain stories and art based on the characters in their favorite games.  These publications are often produced in small quantities and sold to fans at conventions, by mail, or though specialty shops.  fans in Japan have also produced games based on other popular games that have achieved a cult status.  The Queen of Heart series is one example of fan-produced fighting games that star characters in the popular game To Heart

Oh and the picture has a Comic Party character just so you know (well I think they both are, but I’m not sure).  Though as I said I find this interesting that it was in my text book.  I may later have to dig into this deeper and link it to licenses for games and anime games and it just opens a lot up.