This is a drama CD bundled with the PS2 version of Will o' Wisp, Idea Factory's gothic visual novel. It's not really a soundtrack so much as a voice-acted side story with some background music woven in, part of the Ningyou Sentai Dolls series that came packed with the game.
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The audio leans into that mid-2000s Idea Factory melodrama with theatrical vocal performances and mood-setting instrumental cues underneath. Atmospheric strings and piano float behind the dialogue. Pretty niche even by VN standards.
If you're deep into the Will o' Wisp world and want more time with the cast, this is the kind of bonus material that rewards obsessive fans.