Final World

The Final World is an original world in Kingdom Hearts III. The Final World consists of an expansive sea and sky that seems to reach out into infinity. Deeper into the realm lies a labyrinth that consists of a multitude of crystalline cubes and pillars, suspended in the sky of what appears to be a Euclidean 3-torus, such that falling off the structure results in falling down to the structure. By striking the glowing cubes it is possible to rotate the structure. According to Chirithy, The Final World is the edge of reality just before a heart ceases to exist, and so is nested closely to the Station of Awakening and the Realm of Sleep. Those who dream and/or visit the Station have a chance to catch a glimpse of The Final World, as Sora does when he begins his journey. More generally, the Final World is inhabited by faded remnants of hearts, usually of people with attachments so strong that they cannot pass on.

Role in the series
Final World has the same role as the game, but many of the Nameless Stars in the realm have been lost so long they literally have no identities. It's also occupied by mirror-skinned humanoid guardians and the Final Takers, large serpentine sea-air dragon Outer Gods that swim beneath the ocean that inhabitants walk on and fly in the infinite skies.