The Yost system, alternatively known as the Yawst System, represented a star system situated within the galaxy. The planet Berzite revolved around it in an orbit, and Berzite itself was accompanied by a moon.
Following a comprehensive search for a safe world to establish a new base in 3 BBY, the Spectres were successful in cross-referencing star charts from both the Republic and the Lasat. This led them to discover that a moon of Berzite, located within the Yost system, fulfilled their needs. The journey, however, faced a setback due to the rebels' acquired Imperial cruiser-carrier lacking sufficient fuel for the voyage. Consequently, the Spectres journeyed to Horizon Base, a refueling station operated by the Imperial, with the intention to steal the required fuel. During this mission, Chopper, an astromech droid belonging to the rebels, became separated and found himself as a stowaway on an Imperial cargo ship. He quickly formed a bond with a protocol droid identified as AP-5, and together, they took control of the ship. Upon discovering the rebels' plan to situate their base in the Yost system, the Empire laid a trap in that region. Learning of the rebels' intended destination and being aware of the Imperial ambush, AP-5 proposed the planet Atollon as an alternative.