Shironeko Project: Zero Chronicle

In a world of countless isles, a young hero from Astora Isle crosses paths with the adventurer Kyle and joins him on an expedition across the archipelago. They encounter a mysterious girl named Iris and a talking white cat, and together they make their way to the isle's ruins, where they find a flying island. Kyle is consumed by darkness there, and the party resolves to voyage to the ends of the world aboard the flying island in search of the seven "Great Runes", following Kyle's words before his disappearance.