Early concept art shows that Sora would have originally donned Aladdin-inspired shoes and a more street rat-inspired version of his usual wear when he was in Agrabah, but in the released version he just wears his normal outfit instead.

Early screenshots of the game showed Sora with different clothes that were orange and black and a different hairstyle that was black but with large white tufts sticking out the front of it. This early design for the character also resembles the earlier "Lion Sora" design, albeit without the lion elements.

A Station of Awakening for Alice from Wonderland was originally created and planned to appear in this game and accompany the Belle, Cinderella, Aurora, and Snow-White ones but ended up never being used. Spoiler:With a possible explanation being the fact that Alice, like Kairi and Jasmine and unlike the other Princesses of Heart, was not abducted by the Disney villains at the very start of the game.

If you defeat Maleficent in Hollow Bastion before chasing Pinocchio in Monstro, a set of alternate cutscenes will play out as you progress through the rest of Monstro. The cutscenes where Riku talks to Sora in the first chamber of Monstro, and the cutscene where he talks to Maleficent are both edited out of this sequence.

According to series producer Tetsuya Nomura, one reason that Mickey Mouse's role was limited in the original Kingdom Hearts was because around the same time as its release, Capcom owned the license to use Mickey Mouse for the game Disney's Magical Mirror Starring Mickey Mouse. The developers persisted and were eventually given the go-ahead to add him into the game "as long as [they only had him in] one scene, from far away, as a silhouette, with him waving his hand or something". As such, Mickey only appears briefly and seen from behind near the end of the game, helping Sora and Riku seal Kingdom Hearts itself.

Mickey's perspective of this event also appears in Kingdom Hearts 0.2 Birth by Sleep: A fragmentary passage. The reason that Mickey loses his shirt is to partially keep the continuity of the original Kingdom Hearts that showed Mickey in his classic shirtless look.

In each Dive to the Heart segment in almost every game in the series, there is a disembodied voice that can only speak through text that guides the characters (and thus the player as well) through the tutorial of each game. The identity of these voices has been unidentified in every game but Kingdom Hearts: Birth by Sleep (where it is obviously child Sora) and the first Kingdom Hearts. For the latter, in the Kingdom Hearts Ultimania, Nomura was asked who the voice is for the opening of the first game and he finally gave it's identity as being none other than King Mickey. However, this interview was done in the early 2000's before most of the sequels were produced, so it's unknown if this explanation was retconned or not.

In the Bizarre Room in Wonderland, the fireplace's flames can be "put out" if Sora attacks the fireplace's grated opening with a Blizzard spell, and it can be lit anew if the grated opening is hit with Fire magic instead. Being able to put out the fire makes the second phase of the Trickmaster Heartless boss fight even easier, as the frantic boss cannot light their juggling apparatuses and fling their own Fire at Sora. This is also possibly why the Cheshire Cat gifts Sora a Blizzard spell/upgrade when Sora obtains and shows him at least the Claw Marks piece of evidence during Alice's trail, and also why the grated opening itself is able to be locked onto.

According to a comment in the Kingdom Hearts Ultimania guidebook, Aya Brea from Parasite Eve was originally planned to appear in the game as a member of Leon's group. Partway through development, however, Aya was replaced with Aerith Gainsborough from Final Fantasy VII due to requests from staff members who had worked on Final Fantasy VII.