Birka was a sky island far to the southeast from Skypiea. It is only mentioned in the series and has never made an actual appearance. It is the birthplace of Enel and his followers.
The island shares its name with an ancient city on the Moon, where technology and architecture were highly advanced.
Birka was said to be home to many strong warriors; however, their combined might was nothing when compared to Enel.
Enel, Ohm, Gedatsu, Shura and Satori all had access to mantra; Enel’s mantra was noted to be the strongest due to his Devil Fruit powers, while Satori’s was the weakest.
Their known history is that they were one of three races that once lived on the Moon and aided in the creation of the robot-like creatures named Automata.