The Compendium
Even without reaching for the God Treasure, Ryu instinctively knew that it was empty. It was no wonder he hadn't sensed anything special from it to begin with, it simply wasn't that type of treasure. However, its usefulness, or the reason for its Omniscient Grade, still wasn't obvious even after acknowledging this.
At a surface layer, The Compendium was an encyclopedia, but it was one that was empty until it was fed with a source. Essentially, the ability of this God Treasure was to take a sample of an object, whether it was a Spiritual Herb, a Spiritual Ore, or any other natural treasure, and tag it. It could then connect with the stream of Faith connected to this natural treasure and compile all information that could be found on it and summarize its secrets from most important and foundational, to the most secretive and profound.