"Gundam Reconguista in G" is set in the Regild Century (R.C.), a distant future where humanity has rebuilt civilization after the devastation of the Universal Century. The story centers on Bellri Zenam, a young cadet training at the Capital Guard, a military organization tasked with protecting the Capital Tower, a massive structure that supplies energy to the world. The tower is also a symbol of the connection between Earth and space colonies, which have developed a tense relationship due to resource scarcity and ideological differences.

The narrative begins when Bellri encounters Aida Surugan, a member of the Amerian military faction, who is attempting to steal the G-Self, a highly advanced mobile suit. The G-Self is a mysterious machine with unique capabilities, and its activation triggers a series of events that draw Bellri into a larger conflict. Bellri pilots the G-Self, forming a reluctant alliance with Aida, and becomes embroiled in a struggle involving multiple factions, including the Capital Army, the Amerian forces, and the space-based Towasanga nation.

As the story progresses, Bellri and his allies uncover the truth about the G-Self and its connection to the Towasanga, who seek to reclaim their dominance over Earth. The Towasanga's motives are tied to the legacy of the Universal Century and the secrets of the Capital Tower, which holds the key to humanity's past and future. The conflict escalates as factions vie for control of the tower and the G-Self, leading to battles that test Bellri's resolve and force him to confront the complexities of war, loyalty, and identity.

Key characters include Bellri Zenam, the protagonist whose journey from cadet to pivotal figure drives the narrative; Aida Surugan, a determined and resourceful Amerian pilot who challenges Bellri's worldview; Klim Nick, a charismatic and ambitious Towasanga officer; and Raraiya Monday, a mysterious girl with ties to the G-Self and the Towasanga. The interactions between these characters, along with their evolving relationships, shape the story's exploration of themes such as generational conflict, the consequences of technological advancement, and the search for peace in a fractured world.

The plot is marked by its intricate political dynamics, with alliances shifting and betrayals occurring as factions pursue their agendas. The G-Self serves as a central element, its advanced technology and enigmatic origins symbolizing the unresolved tensions between Earth and space. The series balances its focus on mecha battles with character-driven drama, offering a layered narrative that delves into the motivations and struggles of its cast. Through its exploration of a future shaped by humanity's past, "Gundam Reconguista in G" presents a story that is both a continuation of the Gundam legacy and a standalone exploration of its themes.