This is a story in a setting loosely inspired by the concept of the “Backrooms”, an endless many leveled labyrinth, empty/near empty (at least of other humans, maybe life in general), that exists outside of reality. The first level for example is essentially endless empty office halls. Nothing but endless carpet, white walls and fluorescent lights. Thin halls with occasional wood doors that either lead to empty rooms, more hall, or very rarely, perhaps another level.
Note, this is a setting I am vaguely aware of (partially inspired by the club here, but taking it in another direction) but have read very little about. We are not using the ‘official’ version, but something inspired by the concept, that we will develop as we go. The siblings may or may not be alone, if not, other contact, especially with other humans will be extremely rare and short. They won’t release it, especially early on, but escape is impossible. However they got there, it was a one way trip.
They explore constantly, only finding more and more of the same, oddly never hungry, never needing to sleep (though sometimes choosing to do so, just to rest/‘get away’). Strangest of all, their phones, batteries never going down, clocks never moving. No signal though, unable to access the internet, nor able to call anyone else, other than each other.
It takes a toll on their minds eventually. Little to no other company. No else to talk to, they do not notice at first, but eventually they start to depend on each other more and more, to look at each other differently, the brother starts to stare a little more at various parts of her body he had not before but had on other women, discreetly as he can, accidentally brushing against them occasionally. Eventually, one time she chooses to sleep, he watches her, stares at her and can not stop himself from crossing the line, making the move and after some surprise/confusion/awkwardness, having sex.
The line crossed, they become something of mix of siblings and lovers, continuing to have sex, if only for the brief distraction, brief moments of happiness with no idea if it was possible for her to get pregnant because of it (maybe she will, maybe not, we will figure that out).
I figure they are both teens ideally, or if you consider that a limit, the sister is 18, brother 19 or 20. Neither knows how they got there, or where they are or why nothing is right. All they know (at least after being there a little while) is they only have each other.