>>718926269
Nemlei has said that Burial will not be the happy incest route, because burying your problems only makes them worse in the long run, so you could interpret the vision as "you will use sex to keep eachother close and never resolve your issues which will ultimately lead to bad stuff" making it a natural counterpoint to (soon to be renamed) Cliffhanger, where they only start kissing after they've had a little heart-to-heart.

A second interpretation could be that the Demon is only showing them what it wants them to see. The visions will warn them if they're about to be murdered, because the demon wants them to stay alive, but apart from that they could just be a tool to manipulate them into doing its demonic bidding. Why the demon would want to see them fuck or if it actually has any power to shape the visions remains unanswered.

A third option is Nemlei just wanted to draw Andrew blushing after he witnessed a vision of himself bond burgering his sister.