Eva Silver

The Qwaser in control of the element mercury, known as the Witch of Living Silver, appeared as a fake teacher at a lesson of class 1-A, where she trapped the students thanks to her powers and then had Fumika Mitarai humiliated in front of her classmates, so as to "punish" her and them all for their bullying or indifference to Mafuyu and Tomo being bullied. Initially killed and burned alive by Sasha, she managed to survive, altought greatly disfigured, and recover herself by patching her torn body with those of her clones, Q and R.

She later kidnapped Mafuyu so as to have another confrontation with Sasha, in which Ekaterina intervened as well, pointing out that "Eva Silver" is a mere nickname, and that this Qwaser's real identity was that of Eva Braun, wife-lover of Adolf Hitler. She herself states that being alive and young after so much time is thanks to cloning herself and using her clones (Q, R and S being the latest, from A to P having already been killed) to constantly regenerate herself, and thus fulfill Hitler's ideal of a single, superior entity served by all others. While having Mafuyu as a hostage, she proves no match for the combined strength of Sasha and Ekaterina, and is slaughered for good with her last clone.

Nevertheless, she is one of the Qwasers brought back to life to fight Ootori later on in the story. (From Wikipedia)