Once upon a time, a gigantic rock mass hundreds of kilometers in diameter, hammered into the planet at a carefully calculated speed and trajectory, changed the planet. And time passed....

A world where islands (colonies) supported by long pillars are scattered in a sea of ​​clouds as far as the eye can see . The bottom of the sea of ​​clouds is a world of death with no end in sight, and according to legend, this world and the creatures that live there were once created by ``ancestors.''

However, the pillars that support the island are gradually corroding and collapsing, and Raina , a female swordsman , and her partner, Adolus , realize that if things continue like this, their hometown will soon collapse and disappear. In search of the knowledge and techniques of our ancestors, he continues his quest as a migratory bird (okii) who does not belong to any island.