Maybe by slashing Allen's left eye with his akuma hand, Mana had somehow inserted a portion of the dark matter into Allen. It's like a visible sign of the dark matter in Allen. Actually, here I'm assuming that dark matter = Noah (though I know that it's not the same, but since both can be destroyed by innocence, I'm just going to lump them as one). So if Allen didn't have that scar, he would still possess the memories of the fourteenth. When he plays the piano, it's as if he's activating the dark matter within himself, so the scar is affected by the Noah genes thing and changes shape.
Never mind if you don't understand. By now, even I can't understand what I'm trying to say. >< |