In an interview with the Director of Kingdom Hearts, Tetsuya Nomura, he stated that Cloud's appearance in Kingdom Hearts was inspired by Final Fantasy VII character Vincent Valentine. He also stated that he wanted to include Vincent Valentine in the first game.

The small figurine inside Ariel's Grotto will play a melody ("Who Am I?") from the Final Fantasy VII soundtrack.

In Kingdom Hearts, the title card for Halloween Town contains a faster, pitched up version of Kefka's laugh from Final Fantasy VI. This detail reappears in Kingdom Hearts II, although it is slowed and pitched down slightly to be easier to make out.

Rikku was going to have a major role in the first game. She was going to be a part of Leon's group in Traverse Town and help Sora throughout the game. She was removed because of the similarly-named character Riku, and was replaced with Yuffie. She later appeared with the rest of the Gullwings in Kingdom Hearts II.

According to series creator Tetsuya Nomura, the original data and assets for Kingdom Hearts had been lost, forcing Kingdom Hearts HD 1.5 Remix to be remade from the ground up:

In the original version of Kingdom Hearts on PlayStation 2, Selphie's underwear can be seen as she is sitting down. This was removed in Kingdom Hearts HD 1.5 Remix. However, a glimpse of Jane's underwear can still be seen through an opening on the side her skirt.

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.

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.