Personally, if it were up to me and designing this system of martial arts, I would say the pills are the ladder and the training is the rails. Cultivating means absorbing spiritual energy to a point where it transforms your body and very being, and, while many stories just make their main protagonist zoom past them with fake effort, cultivating incorrectly is suppsed to be genuinely dangerous and life threatening at the worst while potentially crippling and wasteful at the least.
Pills often are some great boon, catalyst, and boost that pushes the target into the next stage-albeit chaotically-with the requirements of being able to form the sudden on rush of energy into a stable foundation. Here is where your innate training from fundamental routine takes over and guides the growth correctly instead of letting it become malformed.
That aside, the fundamentals are weird to me. Skin is for defense-I assume your ability to absorb energy and dmg. Flesh is obvious-your ability to exert force to use. Bone is unique and odd-you want to create kinetic energy that you can use with hurting yourself is what I'm guessing, the difference between a push up and a punch. Finally Blood is likely a closer reference to spiritual energy or Qi and using it like a multiplier on all other fundamentals. Due to my tism latching onto physics surrounding Force = Acceleration × Mass vs Momentum = Velocity × Mass and other pet peeves, I've decided to remake this for my entertainment.
Mainly, though, I just decided that stage 1 is Flesh. Not for strength, but, Flexibility. I want the user to be able to withstand all forms of force, damage, and energy. Be it external or internal. From an opponent or self inflicting. Tensil Strength if anything, but, more so a blank canvas for their developement.
