The Koukai, known as the Yellow Sea, is surrounded by four inland seas: the Black Sea in the north, the Blue Sea to the east, the Red Sea in the south, and the White Sea to the west. Eight of the Twelve Kingdoms border at least one of these four seas, extending from the center like the petals of a flower. The remaining four kingdoms are not part of the central mainland and are isolated by the Kyokai(虚海) (Void Sea) which surrounds the land of the Twelve Kingdoms. The Kyokai separates Hourai from the Twelve Kingdoms and is impossible to sail across.