Shadow (FFVI)
Sayid Jarrah (Lost)
Mandy (24)
I don't suppose the hunters from Supernatural count, do they? They assassinate monsters and demons. >_>
Also, what about the actives from Dollhouse? Their missions are very frequently to kill people, but it's not really "them" that's doing the killing, it's the imprints put in their brains.
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First is mnk'boy'907, who looks fab with her gray skin and grandma poncho/shawl thing~
http://img.imgcake.com/nio/boypngbu.png - Nio