More than 2000 years ago, during the age of Discord and Chaos, DIscord reigned with an iron claw with chaos spilling throughout the land. However, during this time, he created four entities to act as his generals.

Set of the South

Tau of the North

Eris of the East

And Angra of the West

Each of them was born from Discords power and controlled a fourth of Discords world, answering only to Discord himself. As the two sisters rose to power to combat Discord, they fought for their master, and for a time they looked to be on the verge of killing the alicorn sisters; until Angra betrayed his master and siblings.

Years later, ancient history is becoming relevant again as it would appear that an old friend has awoken with the return of Discord.

Crossover tab if for the basis for Angra Mainyu from Type-Moon