Exo-Force is a theme inspired by stories from Japanese manga, anime, and tokusatsu. The theme and its sets are based around large combat mechs (known as Battle Machines) piloted by humans in a battle against the mechanized Devastators, Iron Drones and the Meca One, who themselves possess combat machinery of their own, for complete dominance of the mountain they live on, Sentai Mountain. What lies at the bottom of the mountain was never revealed. The theme lasted two and a half years, as it was introduced in spring 2006 and later discontinued in the summer of 2008.
The story in 2006 is based around the Sentai Fortress, its human inhabitants and the mechanical Devastator Robots that are attacking them. At the end of the 2006 story arc, three of the humans, Takeshi, Hikaru, and Ryo are sent to find the legendary Golden City. Subsequently, Sensei Keiken, Ha-Ya-To, and the other humans travel to the city. At the end of the 2007 story arc, human leader Sensei Keiken is captured by the Devastators. The team embarks on a mission to find him, leaving Hitomi in charge of the Golden City. The team rescues Sensei Keiken from the Devastators and Meca One.
Despite the sets being discontinued, the storyline has developed dedicated followers, who continue the plot through fan-fiction stories.
Most of the Exo-Force sets consist of large "battle machines"; these are high-powered, heavily-armoured exo-suits designed to mimic human movement, and are mostly piloted by a single human or robot. Most of these vehicles use Technic joints to give the mech stability with a wide range of movement, and normally come equipped with a short-range melee weapon—a sword, shield or similar—in one hand and a long range weapon—such as a pistol or laser cannon—in the other. 2006 Sets used only Click Ball Joints, while 2007 sets introduced Ball-Joints. Aside from the mecha there are larger combat vehicles, bases, and remote installations such as gates and towers. Also, all of the final sets released in 2008 included a miniature robot that resembled the mech that it accompanies. These are comprised of LEGO elements rather than taking the form of minifigures.
Power cores: The 2006 sets feature power cores - a light-up brick located somewhere in the mech's chasis and connected to one of the weapons by a fibre-optic cable. This was used to "power up" (Exo-Force's catch-phrase) the battle machines. All of the 2006 sets included a Power core, with the exceptions of a few smaller sets, 7708 Uplink and 7711 Sentry.
Exo-Codes: From 2007 on, the power cores were discontinued and "exo-codes" were now included in every set. These codes could be typed into LEGO.com to unlock downloads and additional set information. The 2007 codes were printed directly onto 2x1 flat tiles and incorporated into the set build. The 2008 codes were instead printed on stickers that can be applied to different brick types in different sets.