Austral Island is located 2,000 km south from Samoa islands. The existence of the island was removed from the official records, and Tagami Yuu made a journey to search for the reason. He sailed for the island with Dr. Waive who was his father's friend, Doris who is the daughter of Dr. Waive, and Captain who is the friend of Dr. Waive. On their way to the island, GAIL, the international conglomerate, and gangster, Cougar Connection lead by Lady Lynx attacked them. They managed to arrive at the island, but suddenly a mysterious monster began to attack them. When they became ready for death, a blue giant robot appeared. It destroyed the monster and saved them. Although it was an existence far beyond human knowledge, it reminded Yuu of something warm and familiar. It was Giant Gorg which is called "Messenger of the God" by the inhabitants of the island. Escaping from the attack of GAIL's assault team, Gorg guided Yuu into the underworld. There, he found alien's relic and an alien who woke up after 30,000 years' sleep. (Source: AnimeNfo)

The story takes place in Japan. The year is 2030 and Earth has been completely overrun by a viral disease named "Gibia" that turns infected people into various different monsters, based on their age, sex, and race. A samurai and a ninja from the early Edo period travel together through time and arrive in a ruined Japan to aid a professor working on a cure for the virus. Together, they fight countless Gibia monsters, outlaws, and other fierce foes on their journey to save mankind.

The Sengoku era gave birth to many historical legends. One of them is Naoe Kanetsugu, the brilliant military general of the Uesugi family. Together with Maeda Keiji, a legendary warrior on the battlefield, who become lifelong friends with each other, they carve out a piece of history in the most dangerous and volatile time in Japan's history. The two men recall their beginnings and the journey they took to get to the accomplished position they now sit at.

The Amanto, aliens from outer space, have invaded Earth and taken over feudal Japan. As a result, a prohibition on swords has been established, and the samurai of Japan are treated with disregard as a consequence. However one man, Gintoki Sakata, still possesses the heart of the samurai, although from his love of sweets and work as a yorozuya, one might not expect it. Accompanying him in his jack-of-all-trades line of work are Shinpachi Shimura, a boy with glasses and a strong heart, Kagura with her umbrella and seemingly bottomless stomach, as well as Sadaharu, their oversized pet dog. Of course, these odd jobs are not always simple, as they frequently have run-ins with the police, ragtag rebels, and assassins, oftentimes leading to humorous but unfortunate consequences. Who said life as an errand boy was easy? [Written by MAL Rewrite]