I see that you are already reading
Claymore, but I did not see
Parasyte on your list. You really need to read Parasyte if you haven't already, (but then again, I think everyone should read Parasyte). The manga deals heavily with what it is that gives a person his humanity, especially as the main character slowly begins to lose his.
There's also an excellent manga about Robert Johnson called
Me and the Devil Blues. The legend of Robert Johnson says that he sold his soul to the Devil to gain his ability to play blues. The art is beautiful, but unfortunately, I don't think it's ever going to be finished. Anyways, in the manga he literally sells his soul and grows 10 fingers on his one hand. I highly recommend tracking down
some of Robert Johnson's music if you do decide to read this manga. (Or if you like some old-timey blues.)
Deadman Wonderland is pretty good too. The poor main character gets his super powers and is sent to super prison all in the same day.
Franken Fran has a lot of short stories that involve transformation. It might be worth a look.
Maybe
Darren Shan? That's actually an English book that someone adapted into a manga...Actually that's a movie now...I read a little bit of the manga and it had very cute art, and I've heard decent things about the book, but I've never seen the movie.
I hope some of those help. I don't know if you have anything in your complete list, so I wasn't able to check. I'll add more if I think of any.
Edit: Me and the Devil Blues is thoroughly dark, but everything else should fit the tone qualification. Franken Fran in particular has some dark humor.
Last edited by peppermintmoose at 7:57 am, Mar 27 2010