Birka

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.

The island shares its name with an ancient city on the Moon.

Residents
In the English dub, the residents of Birka were known as Birkans. This name was not given in the original Japanese version of the manga or anime. This race was first seen in Chapter 241 and Episode 155.

Appearance
Like Shandians and the residents of Skypiea, they are endowed with wings on their backs. However, what differentiates them from the other two races, is the fact that their wings face downward. One notable exception is Enel, who doesn't have wings at all: in place of them he instead has a ring with drums on it.

Residents of Birka are quite various in their appearance. Some of them possess goat-like facial features, such as floppy organs on both sides, resembling goat ears (though they also have normal human ears) and small horns. Unlike those from Skypiea and Shandia, their people tend to dress in long white robes and gowns, or other religious, or partly religious looking attire. This gives them them a religious look to some extent. Their race appears on a drawing in Enel's mini-series, on an image that represented the three races of the Sky Islands; the drawing depicting a race with the same wings. Urouge, a pirate in the Blue Sea, also has a Birkan appearance.

Strength
Birka was said to be home to many strong warriors; powerless before Enel, however.

Enel, Ohm, Gedatsu, Shura and Satori all had access to mantra with Enel's mantra noted to be the strongest due to his Devil Fruit powers, while Satori's was the weakest.

Departure from Fairy Vearth
Their known history is that they were one of three races that once lived on the Moon and aided in the creation of the Spaceys. When resources on the moon dried up, they along with the Shandorians (ancestors of the Shandians) and the Skypieans left the moon and the Spaceys behind. They abandoned their city of Birka to settle life anew on the "Blue Star".

The Tides of History
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.

The End of Birka
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.

Trivia

 * The ancient drawing depicts the 3 races of the sky. However, the drawings also appear to depict a group of people working together towards one goal. With this noted at some point the Shandorians, Skypieans and Birkans may have even been one and the same race (more believable since the Skypieans and Shandians wings are almost identical). Regardless of whether or not they were the same people, to date the history of them separating (or maybe just losing contact with each other) has not been mentioned in the storyline. In fact the only mentioning of a link to the three races past appears to be the Birkan's folklore about the Fairy Vearth.