Saoshyant is the cargo ship which serves as the headquarters of BIS, the player's organization in Zone of the Enders: The Fist of Mars. It becomes mobile later in the game, and even appears on the battlefield as a unit which must be protected.
While it is listed as having a substantial amount of hitpoints and an attack named 'Flare', it is completely incapable of defending itself. 'Flare' is never shown being used and in missions where it needs to be protected, any attacks the enemy makes on the vessel are considered grounds for mission failure.
As noted by Tadamichi E. Yukito, Saoshyant's name translates to "reincarnated savior".