Austral Island is situated 2,000 km south of the Samoa islands. The island's existence was erased from official records, prompting Tagami Yuu to embark on a journey to uncover the reason. He set sail for the island accompanied by Dr. Waive, a friend of his father; Doris, Dr. Waive's daughter; and Captain, another friend of Dr. Waive. During their voyage, they were attacked by GAIL, an international conglomerate, and the Cougar Connection, a gangster group led by Lady Lynx. They managed to reach the island, but a mysterious monster suddenly launched an attack. Just as they prepared for death, a blue giant robot appeared. It destroyed the monster and saved them. Although it was an entity far beyond human understanding, it evoked a sense of warmth and familiarity in Yuu. This was Giant Gorg, referred to as the "Messenger of the God" by the island's inhabitants. After escaping an assault by GAIL's team, Gorg guided Yuu into the underworld. There, he discovered an alien relic and an alien who had awakened from a 30,000-year slumber.