Fans are entitled to fan based games, just as much as they are entitled to fan sites. Theres a limit to what fans are alloud and theres the fact that they can make a fan game but theres the fact that they are not allowed to sell it. If I were to make a fansite its just the same as making a fan game it has information about the theme and has things to do in the theme wich in this case is digimon. The fan can build, remake things but is not entitled to manufacture these fan goods for there own profit. This has ban debated to at many locations and its always ben agreed. Take a look at fpsc people make star wars fan games from that and none of them have ever ben sued. Yes digimon is a trademark name and all content in copyright to the company that invented them. But if they found a fansite for there content they would be happy, not want to sue a person.
A fan game is more of a tribute and a hobby more than a copyright infrigment. Same as if it were a fansite, or a built in fan rpg, like people make rpg mods in html for invision based on digimon, its all free that they make so theres no harm, theres a difference between fan based content and sharing illegaly stolen content, mostly because the fans content are there own content.
Are you saying that games based significantly on an idea and fansites are the same when it comes to copyright? Because they're actually quite different. A game that aims at being a large online game is hardly similar at all, in fact; it is multimedia (graphics, art, music, entertainment) that is downloaded and timeconsuming and attracts a durable community. Companies would rather not games be executed at this scale because they are too distracting from their actual sales. I mean, lets say another Naruto MMO comes out, and this one is officially licensed and is being sold by Nintendo or something, but another online RPG with a large community based on a similar idea is already out but for free and is not licensed. The other competitor is taking away sales from the officially licensed game, the company loses profit, they're not happy.
There's a distinction that must be drawn between "fangames" and larger independent online games. "Fangames" falls into the category of what you would find on, say, Newgrounds; small flash dealies that you play once and there's nothing new or interesting after that. Companies could care less. Fansites are merely beacons for the congregation of fans and they mostly discuss the marketed licensed material released by the company. Companies could still care less. An online game with a larger community on a larger scale is something that is renewed, updated, patched, interesting, engaging, and if it's in comptetiton with an officially licensed game, the companies are not happy, and so they enforce their copyright.
I really doubt your game is gonna affect Bandit or whatever there company is called. Your not much of a threat against them. Worst they can do is stop your work and at that point think about it this way. You have an awesome mmorpg engine that you can work off and make something else, but if you think about it a Digimon Game would inspire people to watch the movies and buy their product so in truth you are helping them. B.T.W Digimon is practically dead....