Lorewalking: The Protectorate

I have long been curious about the ethereals, who first came to Pandaria when the Mists parted. A mysterious group, they are reticent to speak of their history... but I am perhaps more persistent than most in my inquiries. So! Who are these strangers? What do we know of their history? We must piece it together, it seems. But our tale begins in Outland, where a hero joined a group of ethereals in Netherstorm to aid them with their cause.