I've read the manga, and couldn't agree more. On the surface, it looks like just some generic horror series attempting a cheap goth flavor, but it quickly turns into the ultimate cat and mouse game (or is that cat-and-also-cat?) to catch the ultimate murderer. I can't think of any other comic/anime so cerebral and thoroughly thought out.
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No one in the world ever gets what they want,
and that is beautiful.
Everybody dies frustrated and sad,
and that is beautiful.
-TMBG