When Rin was told that he was a demon, he didn't really believe it. Sure, he had what is the shortest temper in all of the worlds, and crazy strength to back it up, but he wasn't that different, right?
The exwires were fighting a horde of demons, and Rin was stuck against a shape shifting demon that somehow fed on one's fear, and then changed into a being of nightmares. If you asked him, Rin would say that he wasn't afraid of anything. If you asked his classmates, they would say that Rin was scared of nothing with mentioning (although Bon would find it amusing to point out .thing Rin was proven to be scared of.). However, when the shapeshifter finally settled into a recognizable form, Rin froze, eyes widening and skin turning ashen.
His fear was himself.
Well, not himself, exactly. He saw what everyone else in the world saw when they thought of the phrase "Satan's son"; a black-haired, snarling teen with flaming cold eyes covered with the cursed fire that killed so many years ago. An expression of uncontrollable wrath and insanity adorned the being's face, giving him a truly demonic look.
Rin stared at the demon. Was this really him? Was this what the world saw, what they imagined when they thought of the name "Rin Okumura"? The looks from his classmates (friends?) and the other exorcists proved the fact. That was what the world saw.
He really was a demon, after all.