An ancient statue's petrified remains harbor the spirit of a great and powerful Oni. The ancestors of the inhabitants of the tiny island Kiryokushima (an imaginary island roughly translated as “mental-energy island”) first encountered the demon when they began to inhabit the land, nearly 800 years before the events of the story. As told by the priestess Ookii-Mune (whose name means “big chest”), at that time Gekido-Jin (“furious man,” roughly translated) ransacked the village, killing any foolish warrior of the mortals whom dared to stand against him. Though the humans did manage to destroy the malevolent fiend several times, the creature returned, each time larger and more powerful than its last incarnation, taking its strength and life from the very soil that it trampled beneath its feet.

Yet hope arrived, in the form of a small mysterious monk. The man was quiet, but possessed unfathomable wisdom and will. The human approached the giant, and willingly gave himself to its bloodlust. Gekido-Jin greedily swallowed the impudent mortal, but failed to realize the consequences of its actions. By giving himself of freewill, the monk was able to fight with the stone warrior's spirit, keeping the hate and malice of the Oni in check. However, through his self-sacrifice, the monk damned his soul to an eternity of unceasing combat. His spirit would only know rest if someone else would take his place, and that is exactly what happened shortly after Godzilla arrived on the Kiryokushima's shore.

The village's very existence hung in the balance, as Godzilla moved closer inland. Only by awaking Gekido-Jin would the island know peace once again. A researcher named Kogenta screamed and pleaded with the ancient spirit to release the Oni to battle Godzilla, and his cries were not unheard. Even though Kogenta was killed by Godzilla, his sacrifice was not in vain as he was able to take the place of the mysterious monk inside the Oni. Godzilla smashed Gekido-Jin's earthly form, just as Kogenta allowed the Oni to once again take control of his own body. The statue, whose hammer now bore the face of his foe, reformed and fought fiercely against his larger opponent, but was burned into rubble by Godzilla's wrath. Each time, the Oni came back, reforming from the land itself, thereby making it stronger and bigger than before. After a few times, the stone demon was almost as large as its saurian opponent. The two masses warred with the strength of a thousand armies. It seemed that there was no end to their hate--that is until, in the throes of combat, they were sent cascading into the waves off a cliff, ending their cataclysmic battle. Godzilla swam away, oblivious to the now doomed spirit of Kogenta. His will was pure, and he had been able to let loose the Oni long enough to drive away the big G. But in return, he would never know peace, for all time. Alone, he would be trapped in the statue’s rock form, gazing into the black, frosty depths of the ocean.