450 years prior to the present, an extraterrestrial force called Efi Dorg invades Earth; the people of Sengoku era Japan dub their mecha and robotic drones as oni.

Yukina Shirahane, daughter of the United Nations Kurobe Laboratory director, accidentally reactivates the cockpit module of the Black Relic, releasing Kennosuke from cryostasis.

Aided by Yukina's family and the United Nations Kurobe Laboratory in adjusting to life in the 21st century, he stands against Efi Dorg's invasion of Earth just as he did in his home era.

Efi Dorg (エフィドルグ, Efidorugu) is an extraterrestrial organization which invaded Earth 450 years ago, and in the present day, its Gezon-Reco Company arrives to follow up on the scout force's progress.

When asked by a UN official if Efi Dorg conquered, Fusunani considered it an acceptable description on the basis of reality operating on the principle of survival of the fittest, with the weak serving the strong.

During a career counseling meeting, Yukina Shirahane learns that she is currently failing at Tateyama International High School, although determined to visit Mars someday.

Minoru Aramata shows Yukina a large black cube and a gigantic geoframe found while excavating for the Kurobe Dam sixty years ago.

The research facility dispatches shield-like geoframes called Dwarves to battle the Cactuses, while director Hiromi Shirahane authorizes pilot Tom Borden and navigator Liu Shenmei in the GAUS 1 to fight the Headless.

Yukina opens the Cube after touching a glowing red panel, revealing Kennosuke Tokisada Ouma, a naked man who kneels and calls her princess.

Sixty years ago, the Cube and the Black Relic were discovered near the Kurobe Dam, where the United Nations built a large research facility to study them.

Despite the Black Relic immobilized and Kennosuke being captured by the United Nations forces, he escapes custody again until Sophie Noël tackles him before two security guards activate a shock collar around his neck.

Kennosuke watches a historical movie about the Battle of Okehazama on television, then chases Yukina's pet ferret Kojo riding on a robotic vacuum cleaner.

After evading the reporters and returning home, Yukina shows Kennosuke a notebook written by Takehito about the Ogres, including a passage on the extermination of the Washiba Clan by a mysterious unknown power.

Forty hours ago, Kennosuke and Yukina were stationed by the United Nations Kurobe Laboratory, where they are the only ones who can operate the Black Relic since it implanted them with nano-machine channels.

While Paula Kowalczyk and Girolamo "Giro" Casiraghi transport the Black Relic to Tateyama, North American Aerospace Defense Command (NORAD) detects another object launched from the alien mothership heading for Toyama.

Following Hedo's suicidal death in the Yellow Crab, the United Nations Kurobe Laboratory assesses that the geoframes that landed in various parts of the world are confirmed to be related to the Black Relic of 450 years ago.

On the Efi Dorg Spaceship, the Gezon-Reco Company, people dressed in battle armor, discuss their strategy of gathering pieces of the legendary Pivot Stone.

Elizabeth "Beth" Butler informs Graham that a geoframe called the Longarm was discovered in North America and has returned to the Efi Dorg Spaceship with an unknown object.

Fusunani tells Carrie Dunham and Heath Kingsley, specialists from the extraterrestrial research division, that he is a border reform officer affiliated with Efi Dorg's Gezon-Reco Company.

The objects they seek are fragments of the Pivot Stone that was broken when an advance team was wiped out 450 years ago by the Black Relic, whose wielder seemingly betrayed them.

Dunham and Kingsley question Kennosuke about what happened 450 years ago, but he mentions that the Ogres destroyed the Washiba Clan's castle and he then fought alongside Yukihime in the Black Relic before her inevitable death.

In order to prevent Kennosuke from sitting like a statue all day, Yukina invites him to hike with her to the secret base where she saw her father's notebook, but all they find is a giant crater.

The Black Relic and the two GAUS units fight to drive a geoframe called the Spider controlled by Efi Dorg officer Mirasa from the urban area.

The other students build a large replica of the Black Relic through the night, while Kennosuke and Yukina bring food for them on the Cube, which is airlifted back to the research facility by a helicopter of the defense forces.

However, Efi Dorg officer Yoruba arrives in a flying geoframe called the Bluebird to check on his comrades, also shooting down a cargo aircraft carrying the replacement parts.

After everyone enjoys a meal cooked by Kennosuke, they then criticize the cosplay fan video edited by Carlos, which blasts heavy metal filmed in a black and white format.

As the battle grows fierce and the research facility soon breached by the Headlesses, the Efi Dorg Spaceship drops many Cactuses, which release electronic parasites that take control of some of the staff.

Before Kennosuke reaches them, Muetta reveals that Efi Dorg plans to use the Pivot Stone to create a wormhole between Earth and its homeland, enabling a correctional fleet to storm the planet and subjugate it.

Meanwhile, Graham and Hiromi lead a small group of troops to recapture the United Nation Kurobe Laboratory from the Cactuses, managing to find the unconscious mind-controlled staff and reboot the control room.

The wounded Lefil reveals to Zell, Kennosuke, Muetta and Hiromi that Efi Dorg will send a larger correctional fleet that would reach Earth in 224 rotational periods.