OoooooooOOOOOOOOooooooooooOOOOOOOooooooooo! I know! Norse mythology, with a bit of other things mixed with it as a base.
Ginnungagap; beggining of the world. Fire and Ice meet, making the ocean and first life etc.
Life exited the ocean in pairs, right? (not saying that this is or is not true) One of the pairs being the Wolf and the Man. Each species being a guardian of some aspect of the world. For the wolves, A white spirit and a black spirit - the white chasing the sun, and the black chasing the moon. If the humans died, the wolves being the brother species would also die, and without such a large aspect of life, the rest of the world. Dragons being the guardians of dark/light magic, but since they died off, the aspect of magic also disappeared. It's said that Fenrirsulfur/Fenrir/Fenris/Demon wolf was a black wolf spirit.
Well, you have the setting; you could have the main character a wolf and the 'Other Half of Me' being a human as brother species. You could have the main character be a wolf and the 'Other Half of Me' being the opposing wolf spirit. Or vise-versa.
Note; This is the setting for another work of art, and where the idea came from. There is a comic with the same base (norse with a bit of other things mixed in), but there are lots of stories based just off of norse. Setting based off of mythology is quite common. The other stuff mixed in just fills in the holes norse leaves to stabilize the setting a bit more. You can reuse the setting without copying the plot; make it your own.