Ajin is a live-action adaptation of a Japanese manga series written and illustrated by Gamon Sakurai. Kei Nagai dies in a car accident, but realises he is a type of immortal known as Ajin (demi-human). Hunted by humans, Ajin is eventually found by the government and used as a subject in cruel experiments. He finds fellow demi-humans along the way as he escapes and goes on the run.

Students, including Aoi Nishino, take part in class and sports activity at a prestigious high school. Aoi Nishino is a member of the school’s archery club. He practices archery studiously and doesn’t socialize much with the other students. His childhood friend Haruka Seno is also a member of the archery club, but she worries about Aoi Nishino. One day, thunder strikes the school grounds. After that, the ordinary lives of the students changes drastically. Many samurai descend on the school grounds. It appears that the entire school has traveled back in time to the Sengoku period. Making things worse, they realize that they are in the time right before the Battle of Okehazama takes place.

In the winter of 2117, a runaway vehicle crashes into the Public Safety Bureau Building. The driver is identified as Izumi Yasaka, a psychological counselor at the Sanctuary, a Latent Criminal Isolation Facility in Aomori Prefecture. But right before her interrogation, Inspector Mika Shimotsuki and Enforcer Nobuchika Ginoza are tasked with promptly escorting Yasaka back to Aomori. What awaits them there is a False Paradise.

In the dawn of the Meiji period, the Gokumonjou, an inescapable prison, has been established in the middle of an enormous lake to counter the soaring crime rates the new era has brought. Serving as the ferrymen are the famous Kumou brothers: the eccentric family head, Tenka; the reckless but noble second son, Soramaru; and the guileless youngest, Chuutarou. In spite of their grim work, the three lead relatively peaceful lives in the ever-cloudy town of Oumi, together with their housekeeper, Shirasu Kinjou. But buried in the long history of Oumi is the legend of the terrifying “Orochi,” a serpentine beast that awakens every three hundred years in a human vessel. Unbeknownst to Soramaru and Chuutarou, the actual job of the Kumou family is to seal the Orochi away before it fully revives—or the world will be plunged into destruction. Amid the monster’s next resurrection, the Kumou family must find the resolve to keep laughing under the clouds.

Year 2116—The Japanese government begins to export the Sibyl System unmanned drone robots to troubled countries, and the system spreads throughout the world. A state in the midst of a civil war, SEAUn (the South East Asia Union), brings in the Sibyl System as an experiment. Under the new system, the coastal town of Shambala Float achieves temporary peace and safety. But then SEAUn sends terrorists to Japan. They slip through the Sibyl System and then attack from within. The shadow of a certain man falls on this incident. In charge of the police, Tsunemori travels to Shambala Float to investigate. The truth of justice on this new ground will become clear.