Lets dissect this technique
"Entities such as solids and liquids, physical entities, and corporeal matter are within this Dantian’s scope."
Objects like weapons, solid and liquid elements like earth release, water release, Wood Release, variants of those techniques, etc.
"This ability extends to physical afflictions such as poisons, toxins, pathogens and generally any other thing that integrates itself within the user’s physical being."
If poison and other biological pathogens enter the body you can remove those entities specifically and not just entities of the body around them. Medical shinobi and puppet using poison can be countered with this technique.
"The external component of this technique takes the form of transparent visual distortions similar in nature and appearance to the voids of kamui though with the ability to vary in shape and size. The shape and size are dependent on the rank of the technique."
shapes: swords, spears, balls, animals, etc. If you think of this technique as: Like Rasengan you have a single shape and there is sporadic chakra spiraling all inside it, our technique works in a similar fashion. Think of the shape and the center of that point is the point where the void is converging/collapsing (like kamui) within that defined shape.
"This technique has the ability to combat against techniques of equivalent rank or chakra input."
Look at the chakra before anything else. This technique follows ordinary rank progression 10 (D), 15 (C), 20 (B), 30 (A), 40 (S). You do not get to arbitrarily get to choose your chakra amount.
Let's look at the restrictions
Note: This technique is learned at genin level and follows similar rules for each rank. Genin can only use D-rank applications, chunin = C-rank, jounin = B-rank (upper) A-rank (lower and middle), Dragon/Head Ninja = A-rank (upper) S-rank (lower and middle), Master Ninja = All ranks.
Note: Genin and Chunin are required to use 5 to 3 hand seals respectively for any application’s external component. Jounin require one hand seal, Dragon/Head, and Master Ninja can use up to B-rank with no hand seals. Contact between user and opponent requires no hand seals.
Note: When using the external component of the Upper Dantian, using the A-ranked and above will render an opponent comatose after two turns. C and B-ranks will simply render one unconscious after 4 turns. Each turn of maintaining drains half the original chakra cost. While maintaining no other application of this technique can be used.
Note: Upper Dantian usages, regardless of the component can only be used once every other turn. A-ranked and above usage requires a two turn cool down.
Note: S-rank applications of this technique requires a one turn cool down for the Middle and Lower Dantian.
Note: To erase completely the existence of oneself or of another the user must use 70 chakra. Unlike the external component where it takes three turns to erase another, the internal component is instantaneous in its nature due to a lack of resistance from the user applying it to themselves. Upon using this advanced application either internally or externally the user will be unable to use any Neidan technique for the next two turns. Dragon Ninja and Head Ninja can use this application twice per battle and Master Ninja 3 times per battle
I highlighted something, find the Ester egg.