A secret government project to open a portal to another planet or realm, it was simple enough, but no one on this super secret black project could have forseen the invasion that came from it. The team that made it back from this world, this realm where dragons, elves, orcs, goblins, and other fantasy creatures that we know as fantasy, are real, had no idea that portals from there would be opened on Earth, to invade and enslave us.
The fighting would be bitter, technology against magic, swords. My character would be a marine corps Lt or Captain leading an attack, and being captured, forced to become the sex slave or concubine to the regions warlord, perhaps in exchange for sparing the lives of my platoon or company, or I would wake up to find that he or she had claimed me and was keeping me as theirs while they were on Earth.
If this appeals to anyone, let me know.