You play Detective Diamond, or DD for short, and together with his overly cutesy blob/rabbit sidekick, you... I'm not sure what you do. At all. I do know that after an amazingly long comic-book style intro, you start out the game being attacked by some kind of monstrous housekeeper. After vanquishing the Hell Maid, I launched into an overworld, where I ran into a cute blonde reporter who apparently killed me.
You can find a walk-through (in japanese) and a fair amount of the CG over at Retro PC98.