A disturbing pair of little twin girls named Q and R ask a policewoman to "punish" them with various sexual torture devices they carry in their bags. When she refuses, Q & R kill her and paint the word "Disqualified" in German on the wall with her blood.
Back at school, the class president Mitarai has a crush on Sasha after seeing him rescue a cat from a tree, and she still keeps the tiny piece of iron he used to do it. While doing some chores, Mitarai runs into Q & R, who are trying to find Sasha as well. She ends up getting freaked out by their advances, when Sasha and Teresa show up.
Sasha buys time for Mitarai to escape and warn the class while he deals with Q & R, but these two girls are difficult to fight as they seem to be able to wield the element of mercury, and any pain they receive only turns them on. As Katja steps in to face the twins, she tells Sasha that the real villain is somewhere else.
Mitarai finds this out when she discovers her class has been taken hostage by Eva Silver, the Qwaser of Mercury. She sets up a trap for Sasha and Teresa, then locks Mitarai in the room with Mafuyu and the rest of the class. As Katja is fighting the unkillable twins outside, Mitarai is being humiliated in front of the whole class until Mafuyu finally stands up for her. Mitarai takes the piece of iron from before and cuts Eva's face with it.
Just as Eva is about to retaliate, Sasha appears in the classroom, having somehow beaten Eva's trap.