 If you liked
Blood+
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 ...then you might like
D.Gray-man
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Both are action series with a darker tone to them, and both focus more on characters and are more character-driven than what normal action series tend to do
When I started watching Blood+, the first thing that came to my mind was D.Gray Man but in a different setting. Both have two parties, the good guys and the bad guys. They both have in common an organization which fights off the antagonists. Another noticeable similarity is the 'monsters' even though they're different, they both are dangerous to humanity and humans can also turn into these 'monsters'.
both are focus on the characters and their development normal action series, and in both the main protagonists have a dark past that still haunts them.
in short both amazing