Synopsis
“Believing light and darkness must remain in balance, Master Xehanort seeks to spark war against the ‘tyranny of light’ to restore equilibrium.
In an effort to undermine Xehanort’s plot, Sora, Donald, and Goofy search for seven guardians of light and the “Key to Return Hearts”, while King Mickey and Riku search for previous Keyblade wielders.”―Kingdom Hearts III press release
After setting off on his new journey in Kingdom Hearts 0.2 Birth by Sleep -A Fragmentary Passage-, Sora, Donald, and Goofy will attempt to search for seven guardians of light and the “Key to Return Hearts”, as well as find a way to restore those in Organization XIII connected to Sora (Roxas, Xion, and Namine). Meanwhile, King Mickey and Riku search for other previous Keyblade wielders (Ventus, Terra, and Aqua), in an attempt to stop Master Xehanort’s plan to “balance” the light and darkness, which will ultimately lead to the final showdown between Sora and Master Xehanort. Following the start of the game, Sora seeks out Hercules and through training regains his lost powers after what happened with Xehanort in Dream Drop Distance, completing his Mark of Mastery and becoming a Keyblade Master.
Kingdom Hearts III will serve as the final chapter of the “Dark Seeker” saga, with Nomura revealing that the plot of the game will pick up “immediately after the events of 0.2 Birth by Sleep -A Fragmentary Passage-.” He also added that the plot will examine the seven lights and thirteen darknesses coming together for the final battle, but that everyone that is expected to fulfill these roles may not.
Plot
Continuing on from 0.2, Sora visits Olympus to ask Hercules for assistance in helping recover his lost strength. They end up helping him stop Hades from taking over the Realm of the Gods with the Titans. Despite the victory, Sora only gets the meager clue to believe with all his might in order to get his strength back. The King and Riku are also badly beaten by the Heartless in attempting to find Aqua, damaging or breaking their Keyblades. Yen Sid instructs them to find Merlin to receive replacements, while giving Sora new clothes and a gummiphone. The gummiphone allows communication across the worlds, mainly between the two groups and Ienzo, who is researching the data Ansem the Wise has on Sora back in Radiant Garden.
At the same time, Maleficent and Pete are going from world to world in search of the Black Box; she believes that a book of prophecies is hidden away inside of it. The Organization is also looking for a “New Seven Hearts”, which Yen Sid believes to be the next hosts of the seven pure lights after the Princesses of Heart were relived of that duty, sans Kairi, who maintained her status. Ienzo deciphers the data, which reveals three hearts are inside of Sora’s own heart; they know one is Roxas, and a run-in with Vanitas has them convinced the second belongs to Ventus. Unfortunately, they are unable to create a vessel for Roxas’ heart, as Vexen has rejoined the Organization to continue his research into the Replica Program.
Ansem, Seeker of Darkness manages to track down Ansem the Wise in the Dark Margin; he kidnaps him, while infecting Aqua with a potent darkness to ensure the Guardians of Light are short-handed. He believes that Ansem holds the secret to finding Subject X, a girl who had lost her memories just as he had; Ansem the Heartless takes his former teacher to his former hideout in Twilight Town, wanting to see the data he has hidden. However, Ansem the Wise is rescued by Hayner, Pence and Olette, who are surprisingly backed up by Nobodies. Hiding a safe distance away, they are greeted by Vexen, who explains he infiltrated the Organization to make amends for his previous actions. He coerces Demyx into delivering Ansem and a replica vessel to Radiant Garden, where he can help Ienzo prep it for Roxas.
Elsewhere, in the Dark World, Mickey is taken captive by a Demon Tower and the now fully-corrupted Aqua, known as Anti-Aqua. Riku holds her and the Demon Tower off until Sora manages to find a way there. They defeat the Demon Tower, and Sora purifies Aqua of the darkness that turned her into Anti-Aqua after a difficult fight against her, and takes her back to the realm of light. Aqua leads Sora to Castle Oblivion, which she reverts back to the Land of Departure so they can wake Ventus. However, Vanitas attacks to claim Ven’s heart. Sora is telepathically contacted by Ven, who tells him he still has the power of waking; he wakes Ven, who chases Vantias off before he could kill Aqua. With their training complete, Lea and Kairi join the group, completing the Seven Guardians of Light. Lea is especially confused by the connections between everyone, including the fact Ven and Roxas look the same.
The Guardians go to the Keyblade Graveyard, where the Organization sends waves of Heartless, Nobodies, and Unversed to wear them down, before Terra-Xehanort arrives and manages to take down Ven and Lea before Donald exhausts himself repelling him with his ultimate spell, Zettaflare. A giant tornado of the Demon Tide scatters everyone to other worlds for the Lich to steal their hearts, killing them off for good. However, Sora uses the power of waking to save them, but Young Xehanort warns there is a steep price for misusing that power as Sora has done to save everyone. Sora had also, unknowingly, violated the Master of Masters’ prophecy regarding the outcome of the Second Keyblade War by preventing Master Xehanort from letting darkness win over light. The restored Guardians return to the graveyard, where they take on the Organization, defeating them one by one. Luxord, Marluxia and Larxene fade away; Luxord gifts Sora a special card. Dark Riku is defeated, with his vessel left behind for Naminé’s heart to use. Xigbar falls into a ravine, leaving a cryptic message. Vanitas fades away for good, while its revealed Xehanort’s guardian holds Terra’s heart; Sora helps restore Terra to normal. Xion’s heart takes control of the replica the past her is using, restoring all memory of her. Roxas revives, helping defeat Saïx.
The Heartless, Nobody, and young selves of Xehanort fight Sora, Riku, and the King; the Xehanorts are defeated and return to their original places in time. Despite this, the χ-blade is forged. Xehanort slays Kairi and opens Kingdom Hearts to reboot the universe and purge it of darkness. However, Sora is able to seal Xehanort within himself, being dragged along to Scala ad Caleum. Xehanort absorbs replicas of the Organization to power up, but is defeated. The rest of the Guardians join them, with the spirit of Eraqus convincing Xehanort to give up as he had lost the chess match they played when they were younger. His injuries catching up with him, Master Xehanort accepts defeat and surrenders the χ-blade to Sora before passing on with Eraqus, who apologizes to the Wayfinder Trio for all the grief he put them through before they got their happy ending. Sora uses the χ-blade and seals Kingdom Hearts with the support of his friends. Despite warning from King Mickey, Sora uses the power of waking to revive Kairi. Everybody goes their separate ways to reunite with their friends and loved ones, such as Hayner, Pence, Olette and a revived Isa and Naminé. Everyone celebrates on Destiny Islands, but as Sora and Kairi share a moment, he fades away as punishment for misusing the power of waking and violating the Master of Masters’ prophecy written in the Book of Prophecies, disappearing to parts unknown.
In an epilogue, Xigbar is revealed to have survived the Keyblade War. He is surrounded by the Foretellers, save for Ava. Xigbar is revealed to be Luxu, and shows them the Black Box.
In a post-credits scene, Sora and Riku awaken in Shibuya. As Riku walks the streets, he is unaware that he is being watched by Yozora, the protagonist of the fictional video game Verum Rex. Elsewhere, the Master of Masters surveys the world, framing the moon above to resemble Kingdom Hearts.