The Mega Drive's sound chip doing things that should be illegal. Shinobi III has one of the tightest soundtracks on the Genesis, every track punching above its weight class with that raw FM crunch. "Japonesque" blends traditional Japanese melodic structures with driving electronic percussion and it sounds absolutely unreal coming out of a 16-bit console.
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"Whirlwind" is pure speed, this relentless rhythm that matches the platforming perfectly. Then "Solitary" strips everything back to this moody, almost contemplative piece that gives you room to breathe. Idaten just goes.
The whole score sits in this intersection of action and atmosphere that most Genesis games never even attempted. If you've never played Shinobi III, the music alone is reason enough to start.