Manga 56529 Bungou Stray Dogs Userrecs

Both feature feature working for a freelance agency of people with special powers in a basically corrupt town. Gangsta gives the impression that it takes place in Italy somewhere while Bungou definitely seems to take place in Japan, but the settings are both vaguely semi-corrupt cities where mafia violence breaks out on a day to day basis, giving the characters a chance to be badasses. Their art styles are rather different, with Bungou leaning toward bishounen-style art, and Gangsta being more seinen, but both are high quality. The abilities in Gangsta are also clearly stigmatized and given a more or less thorough explanation, whereas in Bungou Stray Dogs, the abilities exist with little explanation of their origins and are more like magic. Still, if you like seeing cool guys beat up gangsters with powers (and guns and bombs too!), both of these are great!  

Both are mystery themed stories with lots of dark and spooky stuff in it and also quite a bit of action included too. 

I labelled the animes as similar as well. I've gotta say, when I originally read the manga it gave me the same feel as Black Cat did. There are some character relationships that are the same, such as Atsushi and Kyouka being similar to Train and Eve. There are story elements that have the same feeling to them, though not in a bad "this one copied the other" way. Both of these series are very good in my opinion (many say Black Cat's manga is much better than the anime) and are particularly worth picking up. 

Epic fight scenes! Supernatural ability users that conflict with a dark plot ! Both have crazy plot twists and dark tones.  

Both have badass supernatural characters in an agency and bishounen art styles. In Illegal Rare the characters are actual supernatural creatures (such as a vampire) while in Bungou they are humans who have supernatural abilities. They are both pretty funny and quite enjoyable and if you like fantasy manga with well-drawn characters, some humor and drama and some supernatural action, then check the other out! 

They both center on/around the mafia. Both stories include organizations that employ "the gifted" to complete specialty missions involving targets the regular police force can't handle. Of course, both main characters have secret powers that are insanely awesome yet make them a target as people want their power. All in all, both are great and I highly recommend them.  

- a young boy adopted by an agency/detective office - world has abilities/powers - takes on different cases - supernatural/mystery element