"Undefeated Bahamut Chronicle" is set in a world where the remnants of an ancient civilization have left behind powerful mechanical weapons known as Drag-Rides. These weapons are wielded by individuals called Drag-Knights, who are trained at the prestigious Arcadia Academy. The story centers on Lux, a former prince of the now-defunct Arcadia Empire, who is known as the "Undefeated Bahamut" due to his past victories in Drag-Ride battles. However, after the fall of his empire, Lux becomes a fugitive and is forced to serve as a servant at the academy.

Lux's life takes a turn when he encounters Lisesharte Atismata, a princess of the new ruling kingdom, who challenges him to a duel. Despite his reluctance, Lux defeats her using his exceptional skills, drawing the attention of other powerful female Drag-Knights at the academy. These include Philuffy Aingram, a childhood friend with a mysterious past, and Krulcifer Einfolk, a skilled and enigmatic noblewoman. As Lux navigates his new life, he becomes entangled in a series of conflicts involving rival factions, ancient secrets, and the true nature of the Drag-Rides.

The narrative explores themes of redemption, loyalty, and the consequences of power. Lux's journey is marked by his efforts to protect those he cares about while grappling with the guilt of his past actions. The story delves into the political intrigue surrounding the Drag-Rides, as various factions seek to control their power for their own agendas. As Lux and his allies uncover the truth about the ancient civilization and the origins of the Drag-Rides, they must confront powerful enemies and make difficult choices to shape the future of their world.

The series balances action-packed battles with character-driven moments, highlighting the relationships and growth of its main cast. Lux's interactions with Lisesharte, Philuffy, and Krulcifer reveal their individual struggles and motivations, adding depth to the overarching plot. The world-building incorporates elements of fantasy and science fiction, creating a rich backdrop for the unfolding events. "Undefeated Bahamut Chronicle" combines intense combat sequences with a layered narrative, making it a compelling exploration of power, identity, and the bonds that unite its characters.