Crystalline
Within the human body, there were thirteen total Pulses. Six were known as Body Pulses, another six were known as Qi Pulses, and the final one was the Spiritual Entrance Pulse. A large part of the reason Ryu had yet to breakthrough aside from not having an appropriate cultivation technique was precisely because he felt that these thirteen should be linked in some sort of way.
Though Ryu didn't know much of anything about cultivation after the Pulse Opening Realm, his parents had drilled him continuously about the so-called perfect start. As such, he knew quite well how important opening all of his Pulses was.
Even after killing Death Guard Bhishak, Ryu wasn't exactly proud of himself. The standard of the Higher Mortal Plane was just too pitiful. Many didn't even know that there were six Qi and Body Pulses, and even those that did never dared to open the final two, sticking to four total. There was no need to even speak about the Spiritual Entrance Pulse. It was neglected entirely.