Making a beeline for Destiny Islands (and ignoring the foreteller's reactions of dread and confusion) the intrepid heroes embark on their reckless rescue.
On arrival they are shocked to find the world no different than the shores of the Realm of Darkness. There on the sandy beach, patiently waits the Dark Inferno. It says no words, but it blatantly directs its full gaze towards Riku. Most peculiarly it makes no move to attack, instead making the invitational salute of a duelist. Though thrown off, Riku and Kairi draw their weapons in kind.
Without a body Sora is unable to engage directly in the battle. Therefore it is up to Riku and Kairi to defeat this darkness (testing the experience gained in the sleeping worlds). Throughout the battle the world seems to glitch randomly between its light and dark counterparts.
The duo eventually defeats the heartless, but just as the many times before it begins to reform. Seeing that they would need greater strength, Sora overcomes his trepidation and asks Riku to utilize the King's Key. His friend questions if he's sure, and Sora voices his resolve in reply ("If I have you two by my side, I can face whatever future this leads me to!") This is enough to set Riku and Kairi at ease, declaring that they will finish this together.
Charged by the power of friendship, the destiny trio combines their strength in a singular and all-mighty Trinity Strike, finally sealing Ephemer's heart once and for all.
With the Dark Inferno defeated the unconscious forms of Aced and the Disney duo reappear just up the beach. Kairi and Sora immediately direct their attention to the survivors, but Riku becomes distracted by the glittering object the heartless left behind. The silverette investigates, and is devastated to find the familiar form of his mother's jewelry box. Drawn by his tears his friends realize his heart ache and return to comfort him.
A few moments later their mourning is interrupted by a steady pulse emitting from the object. Confused, the destiny trio opens its lid, so unleashing the reawakened memory that was safeguarded within.
We cut to a memory of an elderly Ephemer and his child sitting on the play island's beach. Having been the first Dandelion to arrive to the world-line he has spent the majority of his life establishing Scala ad Caelum and the keyblade order.
Despite his efforts, Ephemer realized that the darkness of the past was far too pervasive for the young order to defend against. Therefore, in order to keep the worlds safe, he decided the plan to isolate the realm of darkness in the lanes between and seal the doors on both sides.
The founder and his child had finished preparations, but neither was ready to say goodbye yet. So, just as countless others would after them, they enjoyed one final sunset amongst the breaking waves. A dialogue ensues that confirms all that has been previously summarized, as well as the promise that one day it would be set right.
The time comes for the warriors to say goodbye. Ephemer would remain in the darkness and endure for as long as he could while his child and their silver-haired lineage would remain on the islands as stewards of the door, for it is by their bloodline that the seal is controlled. Before he entered the cave where the door is hidden, Ephemer bestows his child with the family crest ring, the same one that would go on to reside in the jewelry box and bestow Riku's party with this memory.
Back to the present Riku retrieves his family and dons it, in recognition of a legacy he never realized before. Also at this time Donald, Goof, and Aced stir. Sora and company finally assist the survivors. Having to break the news of the King's departure with his mage and knight the teens also share in grief.
Such mourning does not last long however, for when Aced fully returns to his senses he notices Sora's presence. Instantly the master flies into a fit of rage and attacks the boy's host. Caught off guard, Riku and Kairi barely ward of his assault.
Once positioned to defend themselves the teens demand to know what's wrong. In reply Aced roars "You fool! You ruined everything! Again!" The man goes on to explain venomously that the sleeping worlds are, in reality, the past. By the mission unfulfilled Sora and company failed to establish THE cornerstone of the universe's history. Now the timeline is collapsing like a Jenga tower, and they'll all be erased along with it.
Sora tries to apologize to Aced, but it all falls on deaf ears. Instead, the once proud and wrath filled champion, merely drops his keyblade and miserably crumbles to his knees. Kairi reaches out to comfort him but the master slaps her hand away.
"If I ever see your face again runt... I will kill you..." Aced decrees neutrally.
Not willing to push the matter further, Riku pulls Kairi back and quietly leaves with his friends in tow. Soon, all that remained on the cursed shores was a broken beast, numbly waiting for the undoing of all things...