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Cultivation Techniques are classified into Heaven, Earth, Profound, and Yellow. Yellow Rank Techniques can only advance a cultivator to Spirit Stream Level 3, Profound Rank to Level 6, and Earth Rank to Level 9.
There are only nine levels within the Spirit Stream Realm. Logically speaking, an Earth Rank Technique should suffice to cultivate to Great Perfection within it.
In reality, this is not the case. An Earth Rank Technique can only enable a cultivator to open up to the 180th orifice, but there are as many as 360 orifices within the human body.
After opening the 180th orifice, if one wants to unlock more spiritual orifices, they must switch to cultivating a Heaven Rank Technique.
