Same as Ronin except done on ONLY THE FEMALE NINJA enemies.
FYI, the "Kunoichi Suicide Queens" achievement was HARD AS HELL, it took me four straight hours attempting it, and then finally getting it. The two best spots to attempt this, is on the level "Doppelganger". Right at the start of the level head across the bridge and here there will be 4 female ninjas, and 4 male ninjas, so you can attempt either, and the other spot is on the "The Empty Seven's Story" once your on the ground level in the big circular area there are waves of Male Ninjas, and after them are waves of Female Ninja's, and of course there is a Ninja Ninja Body-Part poker Challenge on that area, I prefer the "Doppelganger" level however harder to attempt at least if you fail, all you have to do is jump off the bridge to restart the section, opposed to on the other level taking 5-10 minutes to get back to the Female Ninja's.
All credit goes to CrustyDirtDemon, Serious Ninja, KFZ Scubs for their guide on xbox360achievements.org