So...going out on a limb here: What if Aatrox is a demonized Darkin?
So in one thread someone brought up Aatrox relating to Tahm and this horned demon in being a representation of some of the seven deadly sins (Tahm being gluttony/greed (can't remember) and the horned one being Lust which empowers Vayne's own sadistic pleasure).
Aatrox however is a Darkin and Riot wants to make more Darkin. But what if Aatrox is not simply a Darkin? What if Aatrox is the result of being corrupted by a demon, mutating him into something else beyond his winged form? Kind of like Nightmare Tryndamere?
What if Aatrox is the current host/user of the demon of wrath? And Tryndamere is another in a long line of new warriors that become drawn to the demon to challenge its user for the right to become the next one?
TLDR: What if Aatrox's sword is the demon of wrath and it's the reason he's become what he is? Potentially even the cause of the near extinction of the Darkin race?
Tahm is talking to the sword!