Zion is an angelic realm, where warrior angels fly to meet with the hosts of Stygia and defeat them, and guard against those who would do harm to others. Zion is a realm of law and protection, but don't make the mistake of thinking that the angels of Zion are nice. The beings of Zion exist to enforce law and punish transgression.

The Other is a being of pure justice, who exists to punish the guilty. The Other was one of the more powerful beings in Zion. Was. But even beings of order can be "flexible" with the rules, which can bring all the wrong kinds of attention in a realm that views the world in terms of black and white. So it was banished, and forced to find a host. Now it seeks to pursue justice...whatever that means to such a being.