The Final World

The Final World is an original world in Kingdom Hearts III.

Settings and Areas
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, 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.

Kingdom Hearts III
When Sora began his Dive to The Heart, he unknowingly passed into the edges of The Final World, where he fought a semi-tranparent Darkside.

After Sora and his friends were defeated by Terra-Xehanort and consumed by a Demon Tide, he ends up in a featureless plane. After wandering for a while he is suddenly met by Ventus's Chirithy, who is shocked that he retains a faint physical form. It explains that this is a sort of limbo for those who have not been fully claimed by death, but that something is keeping Sora and his friends tethered to the Realm of Light, and that Sora can return to life by collecting the pieces of his body scattered throughout The Final World. He collects the first set in this featureless plane, and is then transported to a floating labyrinth where he collects the rest.

While reforming his body, Sora encounters a multitude of Nameless Stars, the remnants of those whose bodies have faded away but whose bonds with the living have kept some part of them there, waiting for their loved ones to join them. One of these is Naminé's, having been slain alongside Kairi. She explains that Kairi is the one keeping Sora, and thus the rest of their friends, tethered to the Realm of Light, and also that she has made contact with Terra via the Lingering Will. Sora promises to save her and finally thank her in person, while she promises to send the Lingering Will to help when Sora is sent back given a second chance to survive his previous battle. A second star tells Sora thar she is waiting for someone who has been changed beyond recognition and no longer remembers her, but would miss her if they were restored. Sora offers to help the star, and she whispers her loved one's name to him.

After restoring his body, Sora asks the Chirithy why it is there and it explains to him they are waiting for their Keyblade wielder, but does not inform Sora that this is Ventus. When Sora asks how to save his friends, the Chirithy alludes to the power of waking, and instructs him to look for the light in the darkness.