As a person have read a lot of manga, I believe this manga is much better than a bunch of popular shounen out there. But how can it's so unpopular? I just accidentally to found out it even I did quite a lot of deep search for good shounen before.
Maybe it's not really that unpopular, at least, I found this manga at the bottom of most manga website.

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I don't know either. I saw the anime first and loved it, then found the manga which I enjoy even more. Perhaps it's because Yasuda Suzuhito hasn't done much other work as an author before (most of Yasuda's portfolio seems to be as an artist for other novel writers). I think things may begin to change now that Durarara is being made (Yasuda was the artist for the novel series and is the Character designer for the anime).

I suspect the reason this series lacks popularity is that not many chapters have been scanlated.

In other news, this question has been asked for many series, but it's more appropriate when a series has actually died in Japan, but is still enjoyable.

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This signature was recovered from Hades to serve in my rotting armies.

Actually, someone have already scan all 5 english vol, you can find it in some read manga online website such as mangafox.com.

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well i can tell you that by just seeing the cover of the first book I didn't even bother to read the summary, know why? because it just looked like those stupid american mangas~

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Do you mean comic books or manga was published in US. Anyway, it's retarded lol.

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good thing its licensed in my country so i get to enjoy it~