Here’s a concise breakdown of the as commonly presented in such posts: 1. Not a Different Key System, but a Different Stylistic Use Japanese pop music uses the same 12-tone equal temperament and major/minor key system as Western music. However, the harmonic idioms , voice leading preferences , and modal mixtures are distinct. 2. Frequent Borrowed Chords (Modal Interchange) The most defining feature is the heavy use of borrowed chords from parallel minor (in a major key) and from parallel major (in a minor key), far more than in typical Western pop.
It seems you're referring to the post or topic: — likely a discussion or article about how harmonic theory in Japanese music (especially in J-Pop, anime songs, and traditional-influenced modern music) differs from or expands upon standard Western functional harmony.