Hahah, Grargoth. . . . .But never mind that, So. . . . . . You seem to have a sci-fi fantasy setting in mind. Let's see. . . . .

How about a world where humans are the dominant species with the portals and other species are a well kept secret, but enough of the undergovernment knows about them to have created a secret society for dealing with and to a degree, controlling the outbreaks and incidents, with the aid of the church. Both "Angels" and demons are in their own ways detrimental to the humans, and the undergovernment does it's best to keep things to a minimum, but long ago gave up on wiping out the other races or closing the portals all together. However where the portals open have major cities around them, but the church and the secret society only monitor them since many demons and "Angels" are content with the status quo and keep their presence to a minimum.

So, the portals would lead to both the demon's home world, as well as the "Angel's" home world, but they also lead to a few alternate places where other species live, but whom have no knowledge of the portals. These worlds would be mostly peaceful, simple worlds like a peaceful version of earth, middle earth, varingard and the like. The demon would take the boy to one of these to raise him, however because of the way demons work he would have to return to the human's home world every few years, say every 4 years? For some reason or another and maybe one such trip could have an incident, when the kid's 17 or so, which would make them stay there for an extended period of time. The origin wold would be just one of many way station worlds out there, giving us a bit of fun with travel should we want a change of scenery.

Other than that, with the 1800 look, cobble and brick roads, dirt between towns, stone and brick buildings with the smaller villages still made of wood and rough stone. I like the idea of horses still in use, and maybe we could make some interesting looking carts and buggies as we go along. . . . . What kind of house do you see the kid starting out in? Do we want him from a rich family so that he may be recognized later when he returns, or a nobody of humble beginnings?