Summary
Sailor Lethe and her twin sister, Sailor Mnemosyne, make a brief appearance solely in Act 48 of the manga. Hailing from the small, impoverished, and chaotic planets of Lethe and Mnemosyne respectively, the sisters were forced to submit to Galaxia’s rule after she brought death and ruin to their worlds, hoping to find peace under her domination. Sailor Lethe derives her name from a Greek naiad and the river in the underworld where souls forget their past lives before reincarnation. In her debut, Lethe identifies herself as the ferryman of the desert river and imprisons Eternal Sailor Moon at the bottom of the River of Oblivion. She murders Luna, Artemis, and Diana before attacking Sailor Moon directly. The assault is halted by Sailor Mnemosyne, who intervenes after determining that Sailor Moon has suffered enough. Lethe argues that the Ginzuishou, or Sailor Moon’s Sailor Crystal, is the root cause of the ongoing wars and claims that destroying it would bring peace. When Sailor Moon offers her own life to end the violence, the twins are deeply moved by her self-sacrifice. However, they realize that the conflict will persist regardless of Sailor Moon’s fate. Before they can release the Senshi, Sailor Chi and Sailor Phi arrive, insulting the twins as useless fools and stealing their Sailor Crystals, which results in their deaths. Lethe employs an attack named "Galactica Myosotis Alpestris" against Usagi; this technique references Myosotis alpestris, a species of alpine forget-me-not flower.
