Thirteen years ago, Earth faced invasion by the Nefarious Monster Army, swiftly repelled by humanity's defenders, the Dragon Keepers. Since then, every Sunday, the defeated monsters endure public humiliation. Seeking to alter this fate, a lone monster named D infiltrates the Ranger Force.
With aid from enigmatic Ranger Yumeko Suzukiri, D seizes a divine artifact, the sole weapon capable of permanently vanquishing the monsters. However, D's demise at the hands of the Dragon Keepers leaves a void. Now, who will stand against them?