Kyokai

Kyokai (虚海, Void Sea), known as the Sea of Emptiness, a large sea that surrounds the Twelve Kingdoms. Beyond the Kyokai, at the end of the world, lies Hourai. It is impossible to sail across the Void Sea and it cannot be crossed by ordinary means. A Shoku is the only known way to cross.

More immediate to the locality of the Twelve Kingdoms, the Void Sea seperates the four outer kingdoms of Tai, Shun, Ren, and Hou from the eight kingdoms on the mainland.