The Guild Ranking Battle (GRB) is a weekly event held every Saturday (3PM EST) that allows guilds to amass ranking points by killing the mobs and bosses found in an instanced battlefield and obtain Etin from them as well. All of the kills in the GRB give no experience nor drops of any kind except Etin coins and those drop only from the bosses.
To reach the battlefield you need to speak to the Guild Management gatekeeper who will teleport you to the waiting room for the battle. The Guild Management gatekeeper can be found in the main city of map one for each faction ; Reikeuseu and Erina. Once the instance portal within the waiting room opens, you may enter and fight for your guild's advancement.
Amassed points determine a guild's rank when compared to other guilds throughout the faction, important mainly as only the top 30 guilds can purchase a Guild House and it's in the Guild House where the Etin comes into play.
There are 3 zones in the battlefield (1-15, 16-30, 31-60), to enter a particular zone step through the respective portal (Portal 1, Portal 2, Portal 3) with a character of appropriate level. Each zone has a boss within that will cause another portal to open upon their death somewhere on the battlefield.