When I wrote a fan fiction piece, I took the character and I spun him out into his own adventures. I developed different plot lines and other characters in addition to the ones established in the show. I don't know that it is that far from what you were doing other than it wasn't related a game. Whether or not they are similar, it is the same principle. One is leaning on someone else's creation, and the other is creating your own characters, world, and plots without the aid of the other structure. Both can be creative. But only one belongs to you and you alone.