Following the defeat of Emperor Banba and the collapse of the Neo-Human Empire, the psionic superhero Inazuman faces a new and even more formidable threat. College student Goro Watari, who transforms first into the pupal Sanagiman and then into the mature moth-like Inazuman, discovers that the power vacuum left by Banba has been filled by the Despar Army. This ruthless organization of evil robots is led by the dictatorial Führer Geisel and his elite warriors, the Udespar siblings, who possess the ability to merge into a single powerful combatant.

As Inazuman struggles to recover his depleted energy following the previous conflict, he finds himself outmatched and forced to retreat. During this vulnerable moment, he is saved by Arai Makoto, a cynical Interpol agent who is also a cyborg. Makoto brings Goro to a secret underground hideout, where the two form an uneasy alliance to continue the fight against this new enemy. The Despar Army proves to be a more calculated and brutal opponent than the Neo-Human Empire, employing strategies such as flooding operations, missile attacks, and psychological warfare. Goro must adapt to this darker reality, relying not only on his signature transforming scarf and his telepathic flying car, Raijingo, but also on new lightning-based abilities to counter the robotic onslaught. The narrative arc follows this desperate struggle, as Inazuman is pushed to his limits against Geisel's technological warfare, culminating in a final confrontation that determines the fate of humanity. The tone of this chapter is notably more serious and somber than the previous series, with higher stakes and a greater emphasis on the hero's isolation and the cost of his battles.