Sailor Lethe and Sailor Mnemosyne are twin sisters who show up only in Act 48 of the manga. They hail from the small, struggling planets of Lethe and Mnemosyne, which were torn apart by violence and poverty. When Galaxia arrived and brought devastation, the sisters had little choice but to join her ranks, hoping her power might finally bring peace to their worlds.
Sailor Lethe takes her name from the naiad of Greek mythology and the river of the underworld where souls drink and forget their past lives before rebirth. True to her mythological roots, she introduces herself as the ferryman of a desert river. Early in her fight with Sailor Moon, Lethe traps Eternal Sailor Moon at the bottom of the River of Oblivion and kills Luna, Artemis, and Diana—a devastating move that's interrupted only by her sister's intervention. Mnemosyne stops the attack, deciding Sailor Moon has suffered enough.
The core of their conflict hinges on Lethe's belief that Sailor Moon's Ginzuishou—her Sailor Crystal—is the root cause of all the wars plaguing their universe. She's convinced that destroying it will bring peace. When Sailor Moon quietly offers her own life to end the violence, both sisters are moved by the gesture. They realize the hard truth: whether Sailor Moon lives or dies, the fighting won't stop. As they're about to release her, Sailor Chi and Sailor Phi arrive and steal their Sailor Crystals, killing them both.
Lethe's signature attack is "Galactica Myosotis Alpestris," named after an alpine forget-me-not flower—a fitting choice given her role as a dealer in oblivion and lost memories.
Content compiled by AnimeList.moe from publicly available sources.
