Dark Release, or Meiton, is an advanced nature KG which is achieved by combining Katon chakra with Raiton chakra. Dark Release is the use of marks on the user's hands to absorb and store chakra which can then be manipulated in different ways, such as redirecting it at the target or to erect a defensive chakra barrier. The chakra that is released utilizing Dark Release usually appears in the form of blue chakra, which is weak against earth and water, and strong against wind and fire. Dark Release can only absorb raw chakra-based attacks and elements and is unable to absorb solid materials, although it is still able to absorb chakra that is present in more solid elements. Dark Release is a rare element that is not seen often in the Ninja World. Meiton is a KG in which the user acts almost as an Organic Fuuinjutsu of sorts, absorbing and releasing physical and spiritual energies (chakra). Because it works, in a sense, like a Fuuinjutsu, the absorbed chakra doesn't actually enter the users Chakra Circulatory System (like what happens with the Rinnegan's absorption abilities) but its kept in the KG mark, as if stored in a separate space within the body. One can say the squares (upper and lower) are much like portals to the sealing space but the sealing space has no connection with the user's chakra. Because of this, the user has little control over the form he can release said chakra. As he releases it, it manifests in a raw energy form rather than a specific elemental one.
Dark Release is strong towards energy based elements because energy absorption is the core ability of dark release. Not only that but Energy is easier to absorb and manipulate than matter. Another thing, Dark is able to absorb things like; Storm, Dust, Scorch and even raw Sage Jutsu. But when release your opponents technique, if your opponent blocks using any of the following; The four obvious ones; Fire, Wind and Raw chakra along side these more uncommon ones; Sand, Rain, Steam or Boil you will have the upper hand, since dark just eats right though energy based chakra. While Dark isn't strong against Water and Earth since they are both matter elements and just doesn't work like that. Earth suffers double strength towards the absorbing ability of Dark Release (meaning that only an S-Rank Dark release can absorb a B-Rank Earth technique)And again when release your opponents technique. If your opponent blocks using any of the following; The two obvious ones Earth and Water as well as; Solid Ice, Steel, Wood or Lava. They will overpower your dark as they are matter based.