SPOILER FREE REVIEW
Girl may kill is a "drama" using mafia ambientation,if you're expecting blood and a show of extreme violence in each chapter, just calmn down, this manga is not a gore thing. But a good drama need good characters and this manga fail on it. It's a cool to spend some time, but nothing great.

Story- 7
The idea of use mafia to create situations of conflict and exploring the dangerous aspect of this side of society is pretty well made, the reader understand that the characters are in a dangerous place and their life is in a constant risk, however the story doesn't have a defined plot, an end to aim, we only know a bit about Mei's goal and the others characters just follow the mood. The author make very strange moments, the characters take unatural actions without much background to explain it and the end is just ???? YOU DON'T THROW AWAY THE WHOLE NARRATIVE PROGRESSION IN SUCH A SIMPLE AND INCONSEQUENT WAY it looked like the manga was canceled or the author get tired of it, but the final makes sense with the "Scorpion and the frog" story of the beggining of the manga.

Art- 4
It's not bad, but is nothing special and the scenes of fight seems "steady" to much to a person in movement.

Characters- 5
The characters doesn't look like humans many times and are hell weak.
Gohongi: The nice guy, with some values but with ??? motivations, but the author uses him in a good way to show the perspective of a normal person in such extreme scenario.
Mei: She has a motivation in the manga and guide the whole narative. *****SPOILER But damnit she throw it away, her goal is what made the story go for 19 chapters just to vanish in a strange manner and after that the thing get out of hand.****** END OF SPOILER
Katsura: Exists to be our hotblooded onee-chan.
Kuzuki: A good oldlady i like her, one of the few "normal" person here.
Ristu: She's here just to create conflict to others characters solve.
Manome: A good guy, but one detail of his past just turned the whole series bad :(
The other characters are not so good and have little timescreen, but with a potencial to be good characters if the writer wouldn't have been such a moron creating a plot with such shallow end.

Enjoyment- 6
Even with such weak story the manga is pretty good to spend some time and is cool how the characters deal with this dark side of society.