"Ethereal Extent is derived from the power Upanishad. It's a miniature version of the soul."
"Ethereal Extent is a fantasy world that the warrior creates with his power Upanishad and energy."
"The Ethereal Extent can change unlimitedly under the control of the soul altar. It's not much similar to the soul altar, but it's connected to the soul directly."
"Ethereal Extent can extend forever without any rupture. It can enlarge unceasingly."
"..."
The experts with the Ethereal Extent, including Blood Devil, Fei Lan, Xia Xin Yan, and Fu Wei showed Shi Yan their Ethereal Extent. They told him their own definition of the Ethereal Extent, which they had experienced.
When warriors broke through to the Ethereal God Realm, the first thing they did was to create the Ethereal Extent. Without an Ethereal Extent, their First Sky of Ethereal God Realm wouldn't be complete. And, if only the Ethereal Extent appeared, the warrior could break through furthermore.