The Shadow Galactica follow Sailor Galaxia on her conquest of the galaxy, working underneath her to collect Star Seeds and Sailor Crystals from defeated planets until Sailor Moon, her Sailor Guardians and the Sailor Starlights rally together to defeat her. They pose as the primary antagonists against Sailor Moon and her friends beginning in Act 50 of the manga, for the Sailor Moon anime arc beginning with Season 5, Episode 7, Farewell and Encounters: The Transitioning Stars of Destiny, and conclude the Sailor Moon Crystal franchise with a two-part film series titled Sailor Moon Cosmos the Movie.

As the final villains against Sailor Moon, the Shadow Galactica boasts some strong members among their ranks. From the feline fiend Sailor Tin Nyanko to the memory master Sailor Lethe, ten members of the Shadow Galactica stand as the strongest opponents Sailor Moon must face before thwarting the destruction caused by Sailor Galxia throughout the galaxy.