Ventus doesn't just share Roxas's looks, but also his voices: Kōki Uchiyama and Jesse Mc Cartney. Roxas himself makes a cameo in the secret ending as well.
Riku's voice actors, Mamoru Miyano and David Gallagher, both play the mysterious youth seen on Destiny Islands at the beginning of the game (i.e., a younger Master Xehanort before he left home) and reprise their roles as Riku in the secret ending.
Risa Uchida and Hayden Panettiere make cameo appearances as an older Kairi and Xion.
Blooper: Before fighting the Unversed alongside Mickey in Radiant Garden, if you look carefully behind Aqua, you can see a second Kairi right behind her. This was rectified in HD 2.5 ReMIX version.
Hackers have found remnants of an unfinished world based on The Jungle Book (1967), the one completed room being King Louie's temple, along with a few partially unfinished jungle rooms including the edge of the man-village. They also found the Light Seeker◊, a Keychain for Ventus that resembles Mickey's Kingdom Key D. It can still be accessed using cheat codes, but only in the Japanese version.
Pleakley was originally going to appear in Deep Space. An untextured model for him remains in the game's code.
Certain cutscenes which appeared in early trailers - shown at events such as the Tokyo Game Show and Jump Festa - were later altered for the game's final release. For example, the scene in which Master Xehanort reveals his plan to forge the χ-blade to Ventus originally took place in Olympus Coliseum, rather than the Keyblade Graveyard (these scenes can be chalked up to assets for new locations introduced in this game not being finished yet). A scant few scenes were also omitted, including one where Terra watches a young Sora and Riku partake in a swordfight, as well as individual lines, such as Terra telling Aqua that searching for the light Master Xehanort is after will lead them to him or Ventus at Destiny Island telling Aqua to erase him.
A texture for a large Treasure Chest for the Land of Departure appears in the game files, but does not appear in-game.
Executive Meddling: Two changes were made to a couple story endings because the producers thought the original plans ended on notes that were too depressing. The Final Episode was originally part of Aqua's story but split off into its own scenario, while the scene where Ven is absorbed into Sora's heart was given a framing scene with Sora and Riku on the beach.
Fan Translation: With the original Japanese PSP release of the Final Mix version of this game. Like Kingdom Hearts II Final Game, this game has an English patch courtesy of Key to Truth.
Bret Iwan replaces the late Wayne Allwine as Mickey.
In the Japanese version, Captain Hook is voiced by Naoya Uchida instead of Chikao Ohtsuka, presumably because the latter voice actor was also voicing Master Xehanort.
Though Hayden Panettiere reprises her role as Kairi, she also replaces Alyson Stoner (who served as her Other Darrin for Kairi) as Xion, making her the Other Darrin to her own Other Darrin.
The HD 1.5 + 2.5 ReMIX release replaces David Gallagher and Mamoru Miyano as the younger Xehanort with Ben Diskin and Takanori Okuda to maintain vocal consistency with his appearances in Dream Drop Distance onwards.
Vanitas was specifically created to invoke this. Miyu Irino—Sora's Japanese voice actor—wanted to play a villain for once. Haley Joel Osment is not known for playing villains either.
Real-Life Relative: Chikao Ohtsuka was chosen as the voice of Master Xehanort specifically for his relationship to Akio Ōtsuka, the previous voice of Xehanort and Ansem, Seeker of Darkness, who is actually Master Xehanort in Terra's body.
Josh Keaton returns as the voice of teenage Hercules after first voicing him in 1997. Also counts as The Original Darrin since teenage Herc was voiced in the animated series by his adult voice actor Tate Donovan.
Despite his falling out with Disney over the development of Bolt, Chris Sanders returns as the voice of Stitch from Lilo & Stitch. In fact, every Lilo and Stitch character in the game is played by their original actor, a first for the series.
Serendipity Writes the Plot: The secret endings of Kingdom Hearts II that tease this game show the three protagonists wearing armor with capes. The capes were intended to be in the final product from the start, but had to be removed because their animations caused FPS issues during multiplayer.
This is one of the last two games in which Alan Young voiced Scrooge McDuck before his death in 2016, the other being the 2013 remake of DuckTales.
This is also the final time David Ogden Stiers would ever voice Jumba Jookiba before his death in 2018.
Throw It In!: According toTetsuya Nomura, the reason Vanitas looks like Sora was because his Japanese voice actor had always wanted to play the role of a villain.
Nomura considered showing Leon and Cloud's past in the game. He decided against it because Radiant Garden was already showing the past of seven Organization XIII members, so including the Final Fantasy characters on top of them would have overloaded the world with too many characters.
A world based off of The Jungle Book world was going to be featured, but was pulled out. It was likely cut due to legal issues with the late Louie Prima's estate, as the character King Louie is a caricature of him.
Laguna from Final Fantasy VIII was meant to appear as the head of the Mirage Arena, but was kept out due to his appearance in Dissidia 012.
Pleakley would've made an appearance in Deep Space.
The Blob Mob was originally a boss, but it was reworked into a normal enemy due to issues with how many bosses were in the game.
The "Birth by Sleep: Volume Two" secret ending of Final Mix hints at a sequel for the PS Vita, though it was axed because the producers thought that there were too many portable games in the franchise. Ideas from the proposed sequel were later reused in Kingdom Hearts 0.2: Birth by Sleep -A fragmentary passage-.
The first trailer shown at Jump Festa 2008 had a lot of scenes that weren't in the final game, or took place differently. Those scenes include Terra thanking Ventus for saving him from an unspecified incident at the Maw of Radiant Garden, Ventus talking to Xehanort at the Olympus Coliseum, Terra watching a young Sora and Riku sparring, Terra defending Ventus at the Maw instead of the Land of Departure, and Ventus requesting Terra and Aqua to erase him at the Destiny Islands instead of the Keyblade Graveyard. Most of these can be chalked up to the assets for the new worlds like Land of Departure not being done at the time of the trailer's release.
The Jump Festa trailer features a scene where normal-sized Ventus sees Cinderella arrive at the ball; in the final game, Ven exclusively explores Cinderella's house at mouse size and cannot visit the palace.
Another Titan from Hercules was considered to be added as an Optional Boss in the Final Mix version instead of Monstro.
Haley Joel Osment's sisterEmily Osment was at one point rumored to voice Aqua.
Word of God: Following the game's release, an Ultimania interview with Nomura was released to explain certain things that happened within the game
The encounter with the Superboss called Unknown is canon for all of the characters. It's supposed to happen just before each character heads to the Keyblade Graveyard for the final time.
Nomura confirmed that the culprit who stole Aurora's heart was actually Master Xehanort and Maleficent, since only beings of darkness like them and the Heartless are able to steal hearts.
Each Unversed embodies a negative emotion, with the Flood representing irritation.
The hero that Zack says Terra reminds of him is Sephiroth. Since this game takes place a decade before the character appears in KH1 and KH2, it is unclear if Sephiroth was a being of darkness at this point.
Despite not being an official master like Aqua, Terra has met all the necessary qualifications of being one, which is why he was able to perform the Keyblade Inheritance ceremony with Riku.
When Kairi touched Aqua's Keyblade, it unintentionally triggered the Keyblade Inheritance Ceremony, passing the ability to wield a Keyblade to Kairi.
Notably, Donald and Goofy are at the Mysterious Tower, despite not recognizing it in KH2 which is set ten years after this game. Nomura jokingly stated it was because the floors are constructed differently.
When asked why Xemnas doesn't seem to wield a Keyblade when his human self could, Nomura stated that it was possible that he use a Keyblade, but intentionally didn't for some reason.
based on The Jungle Book (1967), the one completed room being King Louie's temple, along with a few partially unfinished jungle rooms including the edge of the man-village. They also found the Light Seeker
