I have a little "schizo" theory related to the whole DLC.
Hear me out, The Tao Trio are mostly based around the story of the Two Contraries. The Two Contraries are a pair of dragons in alchemy, named Sophic Mercury and Sophic Sulfur. They are commonly depicted as a white, fluffy dragon with two wings and a black, scaly dragon with four limbs. These depictions heavily informed the body designs of Reshiram and Zekrom. Sophic Mercury is described as active and Sophic Sulfur as passive, which could be a loose inspiration for the truth and ideals that Reshiram and Zekrom represent. The Two Contraries fight because they are opposites, yet they complete each other, similarly to the concept of yin and yang. The Two Contraries are also what allow free will and awareness to exist, reflected in Pokémon by the choice between truth and ideals. In addition, the Three Essentials, mercury, sulfur, and salt, are considered the "child" of the Two Contraries. When the Essentials and Contraries are merged, they become a three-headed dragon. This could be the basis for the original dragon, which split into Reshiram, Zekrom, and Kyurem long ago. (1/3)