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.
When resources on the moon dried up, they along with the Shandorians (ancestors of the Shandia) and the Skypieans left the moon and the Automata behind. They abandoned their city of Birka to settle life anew on the “Blue Star”.
At some point in history, the three races became separated from each other and fell into the individual races. The Birkans settled on a Sky Island apparently named after their former home, Birka. They also appeared to “forget” their origins, although the moon, known to them as the “Fairy Vearth” remained a folk tale amongst their people, believing it to be a place of dreams.
Enel was born and raised on this island, but eight years ago after finding and eating the Devil Fruit Goro Goro no Mi, he destroyed the island with no hesitation, showing no love for his original homeland. Enel then gathered his followers and left for Skypiea and made himself God there.
The descendants of the citizens who left the moon appear to have forgotten their origins, although the moon, called “Fairy Vearth” and believed to be a place of dreams, remains a folk tale amongst the Birkans. Enel, after studying history within the Upper Yard, came to the belief that the moon is the legendary land that he sought: an endless land of sacred dirt, also known as “Vearth”. This is the reason that he constructed the Ark Maxim.
The city, which was in an underground basement within the moon’s surface, has been uninhabited for a long time, and has long since fell into ruin. Despite this, the city retains its advanced look, with the automata being in capsules with inactive electric generators and machinery. The Space Pirates had been digging into the ruins while also warring with the four automata that were created by Dr. Tsukimi.
During his adventures on the moon, after defeating the Space Pirates and gaining the loyalty of the four automata he had rescued from certain death, Enel eventually finds the ruins of Birka, and after reading the murals on the walls, recharges the ancient automata, and decides to settle there.
During the early chapters, it was possible to use the moon to create an estimated time span for Luffy’s adventures, presuming the One Piece world’s time span is equal to that of Earth’s. In some cases, the phase of the moon even gave the chapter its title. Over time, however, this idea seemed to have been retired, and it is no longer possible to use the moon as a time scale.
- Chapter 28 – waxing crescent (moon stage noted in chapter’s title)
- Chapter 95 – first quarter
- Chapter 107 – waxing gibbous
- Chapter 152 – full moon (moon stage noted in chapter’s title)
- Chapter 160 – waning gibbous (still nearly full)
- Chapter 162 – waning gibbous
- Chapter 213 – waning gibbous (heading onto half-moon)
- Chapter 232 – half moon
- Chapter 253 – half moon
- Chapter 334 – half moon (heading to last quarter)
Since the moon is so important there was also one theory that stated that Enel is now controling the moon itself and that that might be Uranus.