* ExecutiveMeddling: It's pretty much clear that Konami lost interest in ''Undying Moon'' prior to its full release. While the game left Early Access, the final version of the game is still incomplete, and most of the content promised in the Roadmap, such as two extra characters, levels and more were not implemented in the final game. Data for it still exist inside the game's internal files, but as of 2024, they're still unavailable. Not only is the game unfinished, but ports for Platform/PlayStation4, Platform/PlayStation5 and Platform/XboxSeriesXAndS were rated early 2022, but never released.
* NoExportForYou: The original game never left Japan, so the only exposure in the West was just at ''VideoGame/CastlevaniaHarmonyOfDespair'' (and Fuma himself only made cameos in Japanese games back then). ''Undying Moon'' averts this and also comes with an emulation of the original game, allowing players to experience the original game, but it was left untranslated, although the PC version can be modded to include a fan-translated rom into it.
* SequelGap: ''Getsu Fuma Den: Undying Moon'' was released in 2022, a full 35 years since the original game. This made it the longest documented sequel gap in the history of video games, dethroning the 30-year gap of previous recordholder ''VideoGame/TheBardsTaleIV''.
* WhatCouldHaveBeen: A proposed sequel, ''Shin Getsu Fuma Den'', has been trademarked as a Platform/PlayStation2 title, similar in vein of ''Shin VideoGame/{{Contra}}'' (''Contra: Shattered Soldier''), but the game was shelved even before it was made. It took until early 2020's for ''Getsu Fuma Den'' to receive a revival just as Konami went back to their PC gaming (and e-Sports) business through ''eFootball'' (''Pro-Evolution Soccer'') and other e-Sports games.
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