Demonic Cultivation

Far beneath the earth is the underworld. It is a twisted place that is very hard to survive in as it is filled with a heavy corrupt Qi known as Ichor. The animals and plants are strange and disturbing things that have mutated to survive in the murky Ichor, and it is overall a very dangerous and uninviting place. Still as corrupt as it is, cultivators are always on the lookout for better Qi sources. And inevitably some learned to absorb and use this Ichor for themselves. Doing so makes them extraordinarily powerful, but also mutates them from human or spirit beast into a demon. Eventually they become entirely reliant on Ichor.
Flesh Fiend (Skill: 10, x4 Combat)
The first stage of becoming a demonic cultivator is to infuse your flesh with Ichor. This gives increased strength and vitality, but by all reports is somewhat painful and leads to berserk behavior.
Bone Fiend (Skill: 15, x16 Combat)
If a cultivator can master themselves however, then the next step is to infuse their bones as well. Ichor infused bones are nearly indestructible and so gives bone fiends incredible resilience.
Blood Fiend (Skill: 20, x64 Combat)
Up to now the process has been a simple one. The only requirement being to ingest Ichor and let it naturally infuse the body. However at this point a cultivator must take Ichor and draw it through their meridians purging lesser Qi and giving them full access to the potent energy. This allows them to regenerate their flesh and use ichor to fuel devastating techniques.
Heart Fiend (Skill: 25, x256 Combat)
At last a cultivator will approach the final area not infused with Ichor, their own soul. Reports at this stage are fragmentary, but scholars theorize that a demonic fiend must compress their soul with Ichor until the two fuse and they form Heart of Ichor. This dramatically increases their already large reserves of Ichor and makes them almost impossible to kill. As they can regenerate anything as long as their Hearts are intact.
Nascent Demon (Skill: 30, x1,280 Combat)
Not much is known about this step as Heart Fiends almost invariably are killed or flee to the underworld. However given the vast difference in power between a Heart Fiend and a True Demon it is theorized that this intermediary step is one where a fiend discards what’s left of their cultivator training and fully delves into the uses of ichor.
True Demon (Skill: 35, x7,680 Combat)
The only observed True Demons are those who have come to the surface because of irritation at demonic cultivators intruding on their portion of the underworld. They are vast things the size of mountains who wield incredible powers. Their size is actually an anomaly as human cultivators don’t grow in size as they become more powerful. Thus it is theorized that these are the demonic equivalent of spirit beasts, and it is uncertain what a True Demon which was originally human would be like.
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Given the similarities to orthodox cultivation scholars are fairly certain there must be stages after the True Demon. However as increasing demonic cultivation requires increasing amounts of ichor anything beyond this point must be deeper inside the underworld where no one has seen them. Indeed there is a rather terrifying hypothesis that the True Demons who occasionally emerge are actually the weakest of their kind. Having been forced to the shallowest parts of the underworld by their peers.