Nothing fancy here, just something that's been lingering in the back of my head since I watched the anime Gate. For those of you who don't know what it is, here's the synapsis from Wikipedia:
When a portal from another world appears in Ginza, Tokyo, a legion of soldiers and monsters emerge to attack the city. Thanks to their far more advanced weaponry and tactics, the Japan Self-Defense Forces (JSDF) easily repels the enemy, passes through the gate and establish a forward base of operations to force the Roman-styled empire of the other world to open peace negotiations. Yōji Itami is a JSDF officer sent to investigate the other world, where magic, dragons and elves are real, using his knowledge of fantasy stories to make his way in this new environment.
Basically as @Keyguyperson put it, its Japanese nationalism at its okayest.
The reason why I'm putting this as a "pre-interest check" instead of a proper one is that I'm doing some other stuff both in RP and irl as well as the fact that I'm still fleshing this concept out some more.
The idea I currently have is that in the far future (2500's) when humanity has spread its wings far and wide and having been once again unified under the banner of Grand Human Union based on High Terra in the Sol System (Earth). A century has past since then and although some resentment between the Loyalists (those who fought with High Terra) and the Revolutionaries (those who fought High Terra and her allies for a shot at their own independence), the human race is once again unified and happy.
However, during a research project into something called the "Arcanum" on the planet of Ennedi, a portal opens up and waves of monsters and fantasy, medieval soldiers pour forth and wreck chaos and havoc on the capital city. However, due to the quick thinking of the local garrison, the invaders were defeated and the portal walled off.
The RP itself would begin as the GHU decides to send troops into the portal proper after several scouting teams have made some runs. I will be making some home worlds which our characters can hail from, each with some special characteristics. Don't worry though, its not going to turn into stat-based, just an outline of what troops from that planet use, specialize in and stereotypically act. I would also allow for characters from the other-side of the Gate to be used, although there might have to be a "waiting period" until those characters will be introduced into the story. Like their sci-fi counterparts, there too will be different kingdoms and such where your characters can hail from.
Now, I know that the biggest question is the tech stuff and how is the fantasy world supposed to survive. Remember the Arcanum thing that triggered the portal opening on Ennedi? The Arcanum is basically a cosmic force that spans multiple universes which allows for magic to be used, the in-game FTL drive, Anima Engines, are actually based on this to some degree. However, only fantasy world characters will be using magic, this is to keep balance and to make sure that the fantasy world isn't completely helpless.
Again, this is just to test the waters and see how many people would be interested. Eventually I'll get up a proper Int Check (assuming this gets enough interest) and explain some more stuff. Most likely the RP itself would have to wait a while as, like I've mentioned, I am busy.