Eva-R

One of the two deranged, ghastly female twins, approximately 12-13 years old, dressed in oddly shaped suits and armed with a wide variety of S&M and erotic devices, such as dildos, pincers and so on. They appeared asking anyone to guide them to St. Mihailov by means of "ordering" them - torturing and tormenting them, otherwise "disqualifying" the ones they asked by brutally slaughtering them. Probably the epitome of perversion of the entire manga so far, Q and R were completely masochistic and capable to derive insane pleasure from their perverse acts, so much so as to cry out of bliss when Ekaterina confronted them and had them impaled by Anastasia.

This revealed the twins to be immortal, as they were capable of regeneration even after the most brutal and grievous wounds in mere seconds, even when killed or torn apart. Being clones of their mistress, they share her power to control the element of mercury. Both Q and R were used by Eva to heal and rebuild herself after her first demise at the hands of Sasha. Another clone, S, appeared during the final confrontation between Sasha and Eva, though she was completely burned, rendering her regeneration useless. (From Wikipedia)