Warning: Unmarked spoilers.
L'erisia and Malchut are embodiments of science and nature.
L'erisia represents science and how it led to progress and destruction. Malchut represents nature and ongoing fight with science. After the final battle between Malchut/A'milia and L'erisia, the world reset with them reincarnated as one being.
They watch over the new world as a balance between harmony and free will. L'erisia and Turii are Wills of the Planet.
Turii is the Will that controls nature and balance, while L'erisia governs sentience and natural selection (i.e. natural disasters). In Aria Te'Laria, Turii's will was contained within the tree and all the Star Children, until Malchut was taken away, at which point the will was transferred solely to her (as the tree and other Star Children died). At that point Malchut lost her memories as a Will of the Planet, and L'erisia could no longer recognize her so they fought. L'erisia started controlling people as an expression of the planet's anger at the Humina having destroyed the Turii tree and thus weakening Her, which also made L'erisia the head of the Consensus at the time. When Malchut "defeated" L'erisia, the planet reset and both of them went back into harmony with the other Wills. Nox is a trans boy.
Since Word of God says that Nox and Matin are a same genetic being sliced in half, they must be identical twins. Identical twins are always born with the same biological sex, so this troper thinks that Nox was designated female at birth, but as he grew up he realized he wanted to be a boy.