Latest manga by Tsukasa Hojo, published in Bunch magazine since it's launch last year. The ongoing series has just reached chapter 28, and 2 tankoubon paperbacks have been published so far, the first of which had already reached record sales of 1.000.000 volumes when the second one came out two months later.
The story is a darker version of City Hunter, set after that series, and according to the author's insistance, is actually an alternate universe of City Hunter, rather than a simple continuation of the story. In this universe, Kaori, Ryo Saeba's partner has died in a car accident, as a result, he has become harder, although he is still chasing around innocent women.
Kaori's heart that was supposed to be used in a heart transplant was stolen en route, and instead transplanted into a young women called Glass Heart, who has been trained to be a serial killer since she was 5, and had tried to commit suicide after her 50th killing broke her heart.
Meanwhile Ryo is still searching for the thieves that took Kaori's heart, believing Kaori lives on in the person who got Kaori's heart. And when Glass Heart wakes from her coma she distinctly remembers strange dreams of a man she doesn't know...
Here's a few links: