The Darkest Passion by Gena Showalter

  BOOK FIVE OF "LORDS OF THE UNDERWORLD"

  The fifth book is about Aeron. He has the Wrath, which is totally uncontrollable if left to act. That's why I don't like it so much, but with the demon, they have a connection and as strange as it may seem, it really exists and is strong.
  In the cover, I like the blue-greenish colour as well as the look on the back of the man, but only to the neck, because from there on I don't like it.
  Aaron has violet eyes, which is so cool, but also a short-cut soldier's hairstyle, which makes me feel angry about the lost beauty. But with him, I wouldn't use that epithet and explain why. His whole body is tattooed (even on the face) and it's rather repulsive, because I may like tattoos, but as long as they are few and meaningful, not another skin painting. Well, his are connected to everyone he killed, so my argument of meaninglessness loses its value, but still, I don't like him being the whole ... this.
  He doesn't want any love and isn't the type of guy who binds. His only closest being is the demon Legion, who is in love with him, but he doesn't perceive her in any other way except as a child. But this demon of hell is a real whimper that is ready for anything to get Aaron, and it really was terrible for me. I actually hate her.
  And then Olivia appears - an angel who has fallen as she has failed in her task of killing Aeron. She is attracted to his beauty and numerous tattoos to remind him of what his demon has done. She's also attracted to its innocence and pure beauty. That's when the darkest passion comes into being. Their love was subjected to no trial, and thanks to that irritating Legion creature, who brought them nothing but problems.
  *I hate it I'm giving a spoiler but... I'm so sad.*
  The only thing I regret is that eventually, it was necessary to come to a very extreme development, again due to Legion and Aeron's fault, to lose his demon forever. Such fury and brimstone couldn't be suitable for anyone else except him. So if we exclude that irritating creature, the book would be better, but alas, it had to be there. Also, Aeron was friends with his demon, he has experienced centuries even millenniums with him and without him... I found him so empty inside, it'd be like tearing apart from you and I'm so sorry for him.