In the fourth arc, Usagi and her friends enter high school and fight against the Dead Moon Circus, led by Queen Nehelenia, the self-proclaimed "rightful ruler" of both Silver Millennium and Earth. Nehelenia invades Elysion, which hosts the Earth's Golden Kingdom, capturing its High Priest Helios and instructing her followers to steal the Silver Crystal. As Prince Endymion, Mamoru is revealed to be the owner of the Golden Crystal, the sacred stone of the Golden Kingdom. Mamoru and the Soldiers combine their powers with those of the Holy Grail, enabling Usagi to transform into Eternal Sailor Moon and kill Nehelenia. Four of Nehelenia's henchmen, the Amazoness Quartet, are revealed to be Sailor Soldiers called the Sailor Quartet, who are destined to become Chibiusa's guardians in the future; they had been awakened prematurely and corrupted by Nehelenia.