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An impish little Russian girl nicknamed "Katja" who appears innocent but is quite domineering in private. Ekaterina is the Qwaser of Copper who uses a copper puppet she calls both "Anastasia" and "Mother" for her own ends.
Ekaterina Kurae (a.k.a. "Katja") is a ten year old girl who was supposedly sent to St. Mihailov Academy as a transfer student from Russia, and also because Miyuri Tsujidou wanted a foreign friend of her own to compete with the bond that Tomo and Mafuyu shared with Sasha. On the outside, she maintains a sweet, innocent exterior as Miyuri lavishes her with expensive gifts. In private, Katja appears to be a domineering, manipulative girl and a Qwaser who has traveled to Japan for reasons known only to her. Despite attacking Sasha shortly after finding him in the country, she seems to be on neutral terms with him, even helping him and his friends out during a few tense battles.
Shortly after arriving in Japan, she made Hana Katsuragi into her obedient slave (which her friend Miyuri doesn't seem to notice), and continues to lord over her in a sort of S&M relationship despite being half her height. She carries a life-sized copper puppet named Anastasia with her in a coffin and sometimes refers to it as "mother," though it is unclear why she does so. However, she manipulates the copper puppet for many tasks ranging from attacking her enemies to simply restraining and teasing her slave girl, even if it does waste her "Soma" to do so.
In later chapters, it is hinted that she might be the reincarnation (or some strange time-warped version) of Tsarina Alexandra, the same one who served as the consort and wife of Tsar Nicholas II before the Romanov dynasty in Russia went kaput. She was also the first one to recognize that the "Queen of the Living Silver" was actually a still-living Eva Braun.