I have contacted the author Nishi and they quoted : "The sound problem doesn't happen in the Korean version, so I do not know how to fix it." and "The reason why I used 溟 instead of 冥 is because the Hades, even though it's an afterworld, it's not all dark and depressing. That's why I didn't used 冥 which means dark."
I've also looked up to see if the music problem had anything to do with Korean characters, but that doesn't seem to be the case. So I really don't have any clue how to fix it... (._.
1) BACKGROUND MUSIC ISSUE: SOLVED
I noticed that in RTP Gamemaker's \Audio\BGM\ folder, the standard resource files are all OGG, in contrast to the game's music files which are all MP3. So I converted the MP3 files to OGG. And now I can hear the game's background music.
I subsequently researched this issue on the internet, & it appears that RTP Gamemaker tends to have problems with MP3 playback during the game for either the game designer &/or the end player. To be on the safe side, it's best to supply OGG (smaller filesize) or WAV (larger filesize), which RTP can natively decode without having to rely on external codecs.
- From gamemaker.info: "If you want to play other files, like mp3 files, you should select the option to use the media player. [...] Preferably don't use mp3 files in your games. [...] Also, not all machines support them. So your game might not run on all machines."
- From rpgmakerweb.com: "the problem might've been the user having set another decoder than default in windows environment to deal with the .mp3 format"
For info, the default MP3 player installed on my system is Winamp (using Nullsoft MPEG Audio Decoder in_mp3.DLL codec). Perhaps RTP Gamemaker or the configuration selected during game compilation does not recognize Winamp's MP3 codec, which is why I couldn't hear the MP3 music during gameplay.
2) 溟 vs 冥: ETYMOLOGY
Thanks for the explanation. If 溟 is preferred, a more effective background reasoning would be take 溟 as a metaphor for the so-called Haenggi Pond of Korean mythology. Since this pond is supposed to be the portal leading to the Underworld entrance, 溟 would thus be the 界 (boundary, realm) that separates the Living World from the Afterlife. Info about Haenggi Pond: Ref 1, Ref 2. However, 溟 (sea, drizzle) itself lacks connotations of brightness, which I think the game is trying to convey.
Personally though, I think 冥 (Hades/ Underworld, dark) works better as the game's title because of the juxtaposition with the suffix 明 (bright, light, to understand). The unexpected & oxymoronic contrast arouses curiosity. And users who played the game would get to see the light, ie. realize that what this 明 is about -- the Afterlife within the game is not that dark, & the reapers aren't grim at all.
For comparison, there is an animated short film (5 mins) with a similar oxymoronic title 'The Life of Death' (2012). It features the reaper/ death's messenger as well, but in another context & setting.