At the first look this anime might be a bit confusing. There are a lot of storylines and many characters with unique background. Every episode is divided to more pieces with a different place, characters and time. But when the anime comes to the final episodes you will notice that everything you saw is perfectly connected and you get a nice final picture of what really happened.
This anime is kinda short and that is very good thing in this case. No useless scenes and filler elements. The characters are really amazing. Just 13 episodes (+3 specials) and you feel like you already knew all the characters for a long time. I am sure that everyone adored Isaac and Miria after watching this haha.
Anyway, the story is very interesting. We can follow the stories of some mafia families and people living around them and in the middle of that supernatural abilities like immortality. You may think that it sounds a bit weird but surprisingly in fits together perfectly.
The art and soundtrack is also very good. To be honest, it has one of the best openings I know. Real masterpiece.