The story takes place in a fantasy world consisting of humans, Dragonoids and Monsters. There is a relative harmony between the three races. There are also Drops, spherical objects that come out of the planet, which can power up the Monsters. Humans and Dragonoids can take on the role of Dragon Callers if they have the capability to see the Drops, wherein, they form bonds with monsters. Currently, the planet is facing Drop Impacts, occurrences where a large amount of Drops are suddenly generated in a single area (and can also spread), which affects the lands and makes the Monsters berserk. In fact, one of the main duties of Dragon Callers is to settle the Drop Impacts by stabilizing the Drop distribution.
The Universal Century, a history marked by space colonization and space warfare, has passed. Humanity's prosperity, which ushered in a new era known as the Regild Century (R.C.), was believed to endure alongside global peace. In RC 1014, Bellri Zenam, a pilot in training of the Capitol Guard is somehow chosen by the G-Self - a highly maneuverable Mobile Suit of unknown origin - to lead to uncover hidden truths that will shake the peace of the Regild Century era.