High school student Koichi Kamiya lives an ordinary life until a mysterious voice calls out to him in his dreams, demanding that he awaken as the successor to an ancient alien legacy known as Babel. This inheritance marks him as Babel II, the latest in a line of protectors entrusted with an immense power called the Babel Legacy. His emergence forces him into a direct conflict with Lord Yomi, a powerful psychic who is gathering other superhumans to dominate the world. Yomi seeks the same Babel Legacy for himself, a power that can only be wielded by the true successor. To fight this threat, Koichi commands the allegiance of three extraordinary beings: Rohdem, a shapeshifting black panther; Robross, a giant, pterodactyl-like bird; and Poseidon, a colossal humanoid robot that rises from the ocean depths.

The series follows Koichi as he grapples with his new identity and the immense responsibility of being Earth’s defender. His journey takes him from the deserts of southern Asia to the streets of Manhattan, and ultimately to a hidden base in the Swiss Alps. Koichi is not alone in this fight; he receives support from Reika Saeki, an agent of the UNIAS who is also trying to stop Yomi’s organization, ADES. This group controls significant political and economic power around the globe. Among Yomi’s key lieutenants are Leon, a student council president at Koichi’s own school who harbors a deep hatred for humanity, and Ferris, a cold and calculating woman who uses poisoned needles as weapons.

A major narrative arc involves the history of Babel I, the alien who first came to Earth five thousand years ago and attempted to build a great tower to signal his people. This failed project left behind the Tower of Babel, a hidden base in a forgotten desert that contains the central computer, Urmintul. The computer reveals Koichi’s true origins and his mission to protect the planet. The conflict intensifies when it is revealed that Lord Yomi is also a distant descendant of the original Babel, making him a rival heir with psychic powers equal to Koichi’s own. Their struggle becomes a clash of siblings for control of the Legacy. The story culminates in a final showdown within the Tower of Babel, where the fate of the world hangs in the balance as the two powerful psychics battle for ultimate control.