 If you liked
Girl May Kill
|
 ...then you might like
Candy & Cigarettes
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The killer in both of these manga is a young girl who is good with both gun and knife.
While the protagonist in Candy & cigarettes is a old man who had been a SP before joining the agency fighting alongside the shoujo killer, the protagonist in Girl May Kill is a random young man who is dragged into the incident.
Both stories are entertaining to read. Although some of the plots may not be realistic enough, the element of fantasy is just nice for most readers.