During his latest interview with Dengeki PlayStation magazine, Tetsuya Nomura revealed that Kingdom Hearts 0.2 Birth by Sleep -A Fragmentary Passage- was originally intended to be included in the beginning of Kingdom Hearts III. He further explains that one of the reasons it became its own game is due to an increase in material for Kingdom Hearts III.
A quote from the interview can be found below, thanks to Kayla Copeland (email@example.com) for the translations.
Nomura: Actually, this was what I worried about the most. We showed this for a bit in the secret episode of [KHBbS FM], but the concept for two chapters of [BbS] is something we've had for a while, and because of problems with time, it's become just a morceau. That concept itself is living on as a setup, so it was our plan to show it at the beginning of [KHIII], but since the volume of material in [KHIII] has increased, I was thinking it was something we just touched on a little. Just as I explained in your previous question, we won't show the whole thing of the initial concept, but we decided to show it ahead of [KHIII] as a short episode.
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