Mason is not imaginary.
He's not a ghost, either.
And he's definitely not a hallucination.
Mason is the one Aerling capable of saving an entire world.
He thought he was going home, but surviving Sentinel attacks and making it back to the Aerling world is only the beginning of Mason's fight to protect the ones he loves. Every Aerling believes he can save them, but in order to win a battle that has been raging for millennium, Mason must face down the one man he truly fears, the only man capable of withstanding his power. This is one fight Mason may not be able to win.