Mnemosyne
Mnemosyne (ムネモシュネ) was a planet mentioned only in the Sailor Moon manga and Sailor Moon Crystal. The only information given about the planet was that it was located somewhere in the Milky Way, and that it was the original home planet of Sailor Mnemosyne. This planet was at war with the planet Lethe, and was destroyed during Sailor Galaxia's conquest of the galaxy.