I have a theory that the Sirens were created by Atlas. Back when Atlas first discovered Eridian Technology, they conducted experiments to see how the Eridian energy could effect the human physiology. When it was determine that casual exposure to the energy was seemingly harmless, the human test subjects were sent free. It wasn’t until the former test subjects started having kids did the Sirens began to appear. After Atlas went bankrupt and Eridium began to appear, Handsome Jack resumed the experiments for higher exposure and created mutants like the Rats.
“I was kinda surprised when I found out Japan hated Avatar the Last
Airbender, the reason why because Fire Nation was heavily influenced by
Imperial Japan and Japan doesn’t want to be reminded the war atrocities
they did in World War II. But Japan manage to like Legend of Korra.”