The person is so obsessed with a game series that he creates a totally new story with new main protagonists but some of the names of characters, places, objects and weapons are still the same as it was used in the game.
Answers (2)
Doing that would fall under the category of fan fiction, provided the author doesn't make money off of it. However, if you create you're own world, characters and use elements inspired by the said game, it could very well be original. Say your inspired by Sonic the Hedgehog to write a story; you could either write a fan fic for your own self amusement using the settings and items from the games. Or, you could set your story in a world inspired by the games but without making it too obvious. Its not easy, but it's not impossible either.