In reality, the world is captured in an hourglass. Every twelve hours, it turns around and sand slips from the one side to the other. First creating earth, then water, then sky, then life. The entire process takes only few minutes and all life loses consciousness during this period.
The sun and moon are the same luminary body, named ‘Lunol’. In contrast to our world, they have the same size, as both the sun and the moon are one half of Lunol. Inside of Lunol, there is another, very small world which exists for the minutes in which the sand gathers before being scattered back into the hourglass. Man, beast, plant, stone and water alike shape one sculpture, the sand castle, the home of Isis and Hedetet. Here, the two sisters inform each other about the happenings on their respective sides of the hourglass. Isis travels with the humans, Hedetet with the grines.
The grine world is a contrast to the human world. It is an immaterial mirror-world to the humans and the other way around. The sands are a mixture of purple and blue, it’s inhabitants look like what a human would describe as a spirit. A grine is a very pale creature, which can be human, animal or even a plant, with a skin that resembles torn clothes which looks as if fluttering in the air. Regardless, grines are very similar to their counterparts in behaviour.
In fact, for every life form in the human world, there is a grine. But the two never contact each other, in a conscious state at least, as they create the sand castle together.
Basically this was what I had for an RP I ran on another site, upon death the person and grine would be reborn, but in each other's world. If the Goddesses didn't judge them worthy they'd become djinns (spirits) forced to forever remain on either bottom or top (so for example human world at day, grine world at night, depending on where/when they died)
And I know Lunol is a lame name, but I don't give a shit.
Other than that, in my current fantasy-style RP I haven't ran into it yet, but as its religion is ripping off Christianity I will prolly do the same to afterlife. In my more modern RP's the afterlife is up to interpretation, but the practice is that the body becomes lifeless, which is all you really need to know to go on ;p