Asebi to Sora Sekai no Boukensha

In a world where humanity lives on islands in the sky and mighty Dragonfish dominate the airspace, adventurers Asebi and Yuu head to Kaiko Island. In search of a map that shows the way to the heart of the legendary empire Voldesia - the capital Blunt! Incredible technical achievements are suspected be found there, because the legendary empire was much more developed than the current society. But Yuu and Asebi are not the only ones who want to go the long and arduous way...