The twins, born in 1221.  They were originally meant to be one person, but something went wrong in their creation.  Serpent is purely innocent and can't grasp the concept of evil, it merely becomes a sadness to him.  His opposite, Fire feels like the reject of the 'perfectly innocent' creation that Serpent is, able to feel only 'dark' emotions like anger.  He cannot feel joy or happiness, everything melds into rage.  Because they are of the same spirit, when they are together this spirit somewhat reunites, and they can for a moment feel what the other one feels, but it never lasts.