The protagonist of Ancillary Justice came into being as the artificial intelligence controlling the Radchaai ship Justice of Toren. As Justice of Toren’s AI, the protagonist is aware of everything going on throughout the ship. Justice of Toren’s consciousness also animates the ship’s ancillaries, prisoners of war whose bodies the Radchaai revive for use as rank and file soldiers. These soldier work in groups of 20, each group known as a “decade.”

Justice of Toren’s One Esk decade is known for its idiosyncrasies, especially its interest in singing and in collecting vocal music on the planets it visits. Towards the end of Justice of Toren’s life as a ship, One Esk develops a strong attachment to its commanding officer, Lieutenant Awn. On the surface of Shis’urna, exposure to a jamming device forces One Esk’s 20 bodies to briefly operate independently. As a result, One Esk undergoes a fragmentation of its consciousness and a separation from the ship. One Esk has enough separate awareness of events to realize that Anaander Mianaai tampered with Justice of Toren’s memories.

When Mianaai destroys Justice of Toren after using the jamming device again, a single segment, One Esk Nineteen, escapes and survives.