vampire juuji kai / record of fallen vampire,

This manga has an extraordinary storyline. if you think of vampires, dhampires, humans AND aliens, it seems too much to be good. but to my surprise, this manga turned out to be really a masterpiece.
The characters have very profound personalities, nothing is just black-white.
The plot releases it's mystery slowly, which gives a very good vibe of curiosity and the urge to continue reading enormous.

I really enjoyed this manga, and I would recommend this as a must to read.