When a colossal space monster attacks a city, chaos ensues as people flee in terror. Amidst the pandemonium, five high school students—En, Kai, Shin, Yoku, and Ryu—find themselves cornered with no escape in sight. Desperate, they seek refuge in a nearby patrol car, only to be engulfed by a blinding blue-white light that transports them to a realm beyond their wildest imaginations. To their bewilderment, they are greeted by an extraterrestrial being known as Bravian, an officer from the Space Police Organization tasked with safeguarding universal peace. Revealing that he is a target of savage aliens imprisoned in the Space Prison Sargasso, Bravian entrusts them with the Dag Beagle, a formidable battle machine crafted from Earth's technology to combat this looming threat. Empowered by Bravian's energy, the students meld with the Dag Beagle to become the valiant warriors known as Dagwon, embarking on a perilous mission to defend against the space monsters. As En discovers his unique connection to the patrol car, he transforms into the formidable Brave Robot Dag Fire, leading the charge against their adversaries. Yet, this epic clash between the heroic Dagwon and the malevolent inhabitants of Sargasso is only the beginning of their cosmic battle for survival.