First off, I watched this with German dub mostly, and while it wasn't terrible, the English one is way superior, and the German...maybe pretty dull. Watch it in English.

The killer B, who is murdering horrible criminals. Actually, he isn't as much as the protagonist as Keith is.

Maybe it was for the German dub, as Keith is way more badass in English voice, but this really took some time for me to kick off. It is all about the climax and ending building up and honestly, in the process - it feels like eventually it was inventing way more concepts for it than necessary. Some parts of the plot were confusing like the whole black wing king something which I felt was never properly explained.

Be like: Hellsing OVAs (less bloody, but all about the climax and ending building up), Darker than Black (same, plus maybe somewhat more similar setting)

Rating: 8/10