Kasumi doens't have a Keikei-Genkai, but she has the abilites over toxins in the air, therefore, she can posses and control posion.
Acid Spit: Converting her chakra nature, she can make her spit acidic and burn of the skin. The most damge is prably 2nd degree burns
Poison Fog: Kasumi make a fog of poison out her mouth. Once it enters the body, it paralzyes the body, leaving Kasumi doing whatever she wants
Radiation Control: Kasumi is able to control and manplutate the toxins within the ground
Code Red: Kasumi bends the toxins around her, and shaped in in a form of a weapon. If the weapon manages to make signifent damge to the body, it but the oppents body in a death-like trance