The FA-100S is a Hyaku Shiki Kai equipped with additional heavy armor. Although its mobility is reduced by the added weight of the Full Armor system, it has an assortment of built-in armaments, including missiles, explosive bolts and powerful beam weaponry. The Full Armor Hyaku Shiki Kai wields a Long Mega Buster, a huge rifle which is based on the Mega Bazooka Launcher used by the original Hyaku Shiki. All these weapons make the Full Armor Hyaku Shiki Kai a powerful offensive unit, albeit a sluggish one.
Though it was not mass-produced due to the trend of variable mobile suits at the time of the Gryps Conflict, the Full Armor Hyaku Shiki Kai prototype unit was used by Cliff Fleming in his fight against a MRX-011 Mass Production Type Psyco Gundam piloted by Enlight near the industrial city Epsilon on the Moon on November 20, UC 0087. With the Full Armor Hyaku Shiki Kai severely damaged and Anaheim Electronics' 3rd Development Division destroyed, the Hyaku Shiki project was officially ended. The Full Armor Hyaki Shiki Kai is last seen in U.C.0096 piloted by Fresberg Squadron member Martin Murtaugh.