You are Aileron.

You are currently staying at your mother's junkyard, and have to share a bed with your eighteen year-old twin sister Apogee.

And waking up with a bad case of morning wood, you are about to experience what sisterly affection really means.

Sequel's HERE!

Disclaimer! Contains: Incest. Go figure.

This story is a spinoff (?) of Dustchu's A Volatile Mixture which, in turn, is a spinoff of Shinodage's ask blog.
[Cue Inception horn]

Credit for the cover goes to Fatcakes! The full picture can be found on her tumblr.