When using the Classic Tone keyblade's Shotlock, Sora actually turns into the same exact cartoony monochrome form that he had donned when he was in the retro Timeless River world in Kingdom Hearts II. In addition, the 'portals' he comes out of and goes into during the Shotlock are extremely similar to the doorways that lead to different areas of the world that are used by the characters in Timeless River's story.
During a scene with the character Demyx, he spouts the line "Yes, Demyx time!" This may be a reference to the web-series "Demyx Time", which released in the late 2000's and followed a cosplayer dressed as Demyx going over Demyx's daily life and events inside Organization XIII.
The team behind Square Enix's Einhander helped develop the expansive Gummi Ship aspect of Kingdom Hearts III. They even included references to Einhander, including an unlockable Gummi Blueprint obtained by scanning a constellation in the Misty Stream area that greatly resembles Einhander' Endymion ship. One of Einhander's bosses, the Schwarzgeist, also cameos as a boss in Kingdom Hearts III, and a remix of Einhander 'Thermosphere' plays when the boss is fought with most Gummi ships. However, if the boss is fought with the Endymion blueprint, then the original PlayStation 1 version of the Thermosphere theme will play.
Spoiler:Scala Ad Caelum, the name of the game's final climactic world, means "Stairway to Heaven" in Latin.
On the game's box-art, the clock on the tower to the left of the characters actually has thirteen roman numerals instead of twelve, and they are out of order. In addition to that, the two hands on the clock are pointing to 13 and the 7, representing the 7 lights and 13 darknesses that play a major role in this game's story. The clock tower itself bears a striking resemblance to the NTT Docomo building in Shinjuku, Japan.
In the Misty Stream area of the game, the player can find a wreckage of a pirate ship which appears to be the Phantom Storm boss from Kingdom Hearts 2, as can be seen by the identical jaw piece.
According to Tetsuya Nomura, the aesthetic and environment design for part of the Hercules-based "Olympus" world was primarily inspired by California's Yosemite National Park, despite, story-wise, taking place in Ancient Greece. This decision came about when co-director Tai Yasue had visited the real-world location.
During a Square Enix Presents segment at E3 2015, Tetsuya Nomura revealed that the kingdom of Corona from Tangled was one of the first worlds to be considered for the game.
The Teacup Attraction Flow was originally going to be in a first-person perspective, however, this angle gave testers motion sickness and was changed to third-person instead.
Kingdom Hearts III is the first Kingdom Hearts game to be on a Microsoft console.