After Kei comes to, he finds out that the Earth he knows has been fractured into many different realities, a majority of the of the planet being controlled by 3 main powers: the Emaan, the Terram, and the Mu.
The Emaan are nearly identical to humans, except for prehensile antenna-like tendrils that come out from the backs of their necks. Emaan males have one, while females have two. They seems to respond and move based on the emotions of the host (like cat ears or dog tails). These tendrils don't exert enough power to actually be able to move or lift heavy objects, so it's assumed that to be some evolutionary artifact. It's mentioned that in the series Emaan acting as spies in Terram have these surgically removed.
The Terram are probably closely related to the humans of Kei's world. The Mu are a robotic race, they were created to serve their creator, but later turned on them and wiped them out.
