SOLVED. A guy is contracted to kill something landed on earth from possibly mars. [s]

[Itadakimasuuu]

I can't really remember much but this guy I think was on mars at some stage or some planet like that but he either gets off or escapes. In the first chapter he kills someone and he had some kind of favourite gun. He is also either biological or mechanically enchanced and the number 13 seems relevant for some reason.
He is contracted to kill these other variants like him who landed on earth and are highly dangerous and falls in love with the woman and she dies and he goes and gets revenge.
Thats about all I can remember, its been annoying me for the last week.

[caracal-eyes]

Thirteen

[Lobstergirl, au gratin]

Itadakimasuuu, was that your book?

[Lobstergirl, au gratin]

No response but I agree this is the correct book. Moving to Solved.