Axel was originally supposed to be killed off in this game. However, due to positive responses from fans, he was kept on.
This game was first solely made for the Japan-only release of Kingdom Hearts II: Final Mix+ (2007). It was later made available in North America as a stand-alone game in 2008. It wouldn't be released in Europe and Australia until the later release of Kingdom Hearts HD 1.5 Remix (2013) which also includes a HD version of Kingdom Hearts Final Mix and HD cutscenes from Kingdom Hearts 358/2 Days.
Tetsuya Nomura had originally planned for Marluxia to be a female so that Larxene wouldn't be the only one. However, he concluded that Xemnas would not want to put a female in charge of Castle Oblivion, so decided to make Marluxia a male instead. Hence Marluxia's pink hair and flower power.
Only the hallways of Castle Oblivion, as well as the Twilight Town, Destiny Islands, and Castle Oblivion levels has new cutscenes created for the remake. Every other level only has worded dialogue.
Due to the aging of Haley Joel Osment and voice changing from puberty, all the sound effects from the original with Sora had to be replaced.