Rock Bird is a city floating in the sky above the Gomi desert. It is also the place of events during chapters 33-53. It is said to be entirely made out of O-Parts. Every fourth year, there is a contest called the olympiad, a contest where O-Part Tacticians fight each other in order to win the rumored legendary O-parts.
The city is controlled by Beelzebub and the entire city is built on his body. But to the people of Rock Bird he is known as Ikaros and is worshipped as a god.
The people of Rock Bird sees most people from the ground as trash and looks down at them. Therefor, they belive themselves to have the rights to dump their trash on the ground. They include losers of the olympiad as trash, but the winners are treated kind-hearted.