Angel Heart

-- Children being kidnapped, brainwashed and turned into unfeeling assassins. -- A male and female assassin pair bonding; their bond being shattered by their organization forcing them to kill each other. -- The assassins having to come to terms with normal life, after previously only knowing a world of murder and death. After an intense opening arc, AH becomes more like City Hunter: the emphasis switching to episodic, more lighthearted content. Phantom, on the other hand, is dark and serious all the way through. 

its similar in that there are people who are young people trapped in a world where they are forced to fight and they cant escape it, gunslinger girls has more action and fighting than angel heart but angel heart has more romance so they are both amazing and moving series. 

The show's around the same time with a similar animation style. Both have characters that wants to come out of the killing world and lead a normal lifestyle. Both have main characters with huge dark past.  

* It is about an hitman * The hitman is emotionless # The feeling is really different as Golgo 13 has sex scenes instead of romance focus # Glass Heart isn't separated in arcs like Golgo 13. Instead, it shows a development in the scenario. 

Both animes involve certain girl who had a heart transplant from a donor who was affiliated with a certain MC and from there they seek out this MC and becomes the replacement of an MC's pervious associated who died.  

Both include female bounty hunters, good stories and similar art style. If you liked one you'll probably like the other 

Both main characters are assassins, leave their organisation and become influenced by the other characters to become "normal" Similar plot layout 

Firstly the main characters are the same archetype - female assassins trained since they were little try to change themselves for the better and fight against who they were fighting for. (I don't consider that a spoiler because that's pretty much revealed in the first few episodes of both series) The art style of both series is similar as well. But what really made me think of Angel Heart as I was watching Ultraviolet was the feel of the show, they both definitely have the same feel. So much so that I looked up whether these two had some kind of relation when I got finished watching. read more 

Both series involve people who live in the underground world. They are filled with characters who are professionals that have great gun skills. Xiang Ying and Revy come from difficult pasts which make them in to the present day them. Both series are filled with action, killings, and excitement. If you like one... you will sure to like the other. 

Basically investigative thematic, and trained "women (not girls) with guns". 

Assassins/mafia