Nova sends dissidents outside the wall as a sort of Fate Worse than Death.
The reason Nyl was checking Piras' father's grave was because she thought that he had really been sent outside the wall as well.- Kinda disproved due to the status that People can live outside the walls
Piras is actually Luke from Tales of the Abyss.
He's a ginger, he has long hair, and he's an airhead. It makes perfect sense! Also, in his dreams he has an evil aberration twin so yeah, the aberration is the real one and he's a clone. Flux can make humans into aberrations.
There are four types of Flux: A, T, C, and R. There are six (known anyway) types of aberration, one of which is called hybrid, and one is invisible. Since aberrations eat other people's flux, this would explain invisible aberrations (along with those who possibly used all energy up), leaving four to form if a user uses Flux too often, and hybrid to form if they use two or more types too often.