Pandora Box

In the World of Build, the Pandora Box (パンドラボックス) is an extraterrestrial artifact which was used by Evolto and Blood Tribe to destroy numerous planets across the universe, determined by Vernage to hail from the same planet as Evolto himself. Following its use to destroy the civilization on Mars, it was discovered by a human astronaut during a manned mission from Earth which directly preceeded the Sky Wall Disaster, over ten years prior to the outbreak of the War.

Discovery and Activation
The alien artifact was found by Soichi Isurugi, who was a crew member of the INSET exploration vessel Prominence during the astronaut's survey of Martian caverns at the time. Upon being touched, it reacted to the human by shedding its stone encasing to reveal its true form, but at the same time, Evolto was released from the box and possessed Soichi. The box was then carried back onto the Prominence and back to Earth. The Pandora Box was believed to have been technology from part of an advanced civilization on Mars.

The Box was not the only foreign object that was brought back from Mars, as the Queen Vernage explained. Her bangle was amongst one of the display objects set to be displayed in a celebratoral return ceremony later on. As Misora Isurugi stumbled upon the items looking for her father Soichi, the astronaut who found the Box, Vernage latched herself onto Misora and removed the essences from Pandora Box, subsequently hindering Evolto's plans, who during the ceremony, dashed forward and tried to activate the box in an attempt to raise Pandora's Tower. However, due to Vernage tampering with the box beforehand, the tower did not rise, and a bright flash of light emanated from the box, generating the Skywall instead, which divided Japan into three sections. On the day known as the Sky Wall Disaster, the box was somehow able to alter the personalities of everyone present at the ceremony, invoking aggressive tendencies into their later developments. As a result, the country itself was torn apart into three districts, each with their own capital and government and pursuing different aims: Hokuto, focusing on social welfare; Seito, focusing on economic recovery; and Touto, focusing on traditional pacifism. The Pandora Box was later kept in a vault in the Touto Institute of Advanced Matter Physics, where it was studied so as to find a possible way to resolve the Skywall crisis.

Present Day
Sento investigated the Disaster using footage from that day and used a light filter software program to discover that the Pandora Box changed colors and jettisoned two of its green panels upon activation, yet retained its shape. This means that the Pandora Box consists of multiple layers of panels that are interlocked to form its shape, yet somehow can retain its same form and size. Director Himuro confirmed to Sento that the Pandora Box has at least two layers in its structure and the green panels that came loose were stolen three years ago. He suspected that either the government of Seito or Hokuto were involved in the theft and the prime suspect is the astronaut who activated the device.

As it turned out, one of the panels was under the possession of Faust. When Masahiro Nabeshima awoke in the basement lab of nascita, he recognised the compartment in the wall used to check for Best Match combinations of the Full Bottles as being similar to the panel he saw in Faust's headquarters. Sento decided to break apart a section of the wall, only to discover that the other missing panel had been in Soichi Isurugi's possession all this while. As Soichi returned from work, Sento confronted him about the panel.

Soichi eventually revealed that he was the one who activated the Pandora Box, but kept his Evolto facade up, saying he had no idea why he did it.

The Pandora Box also resulted in the creation of the Smash organisms through the Nebula Gas produced from the Skywall.

Transference between parties
Seeing it as an opportunity to incite a war so as to push for Touto's use of the Kamen Rider system for military purposes, Gentoku Himuro/Night Rogue began an operation for Faust to infiltrate the Institute to steal the Pandora Box. Though the operation was slightly deviated due to Blood Stalk's intervention, Night Rogue eventually reclaimed the Pandora Box and kept it in a hidden location, unknown to even Blood Stalk himself.

The location turned out to be in a secret basement of one of Namba Heavy Industries' laboratories. Blood Stalk managed to regain possession of the Pandora Box, much to Night Rogue's anger. Blood Stalk, having become Namba's new working partner, kept the Pandora Box in a storage facility belonging to Nanba Heavy Industries. Build managed to overpower Blood Stalk and claim the Pandora Box using his newly attained OctopusLight form, bringing the Box back to nascita, though the Box would end up back in Nanba's possession yet again due to it, along with the Fullbottles, being taken by Soichi, who turned out to be the true identity of Blood Stalk.

It turned out that Soichi had made use of Sento's transformations into Build as well as Misora's power of purifying Fullbottles so as to fulfill his plan of obtaining 10 pairs of Best Matched Fullbottles so as to open up the Pandora Box. Juzaburo Namba, CEO of Namba Heavy Industries, planned to harness the energy source within the Pandora Box to create a weapon more powerful than nuclear arms. However, upon finding out that most of the Fullbottles stolen were nothing more than just fake replicas created by Sento, Soichi decided to confront Sento at the place where they first met each other. Transforming into their respective forms, Build eventually managed to overpower Stalk using his new RabbitTank Sparkling form, created using a component of essence from the Pandora Box. Soichi then decided to leave the Box with Sento once again, saying that he could take it back whenever he wanted to.

War for the Pandora Box
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Losing the Touto Fullbottles secured at official residences to Hokuto, Gentoku deduced there was a Hokuto spy in Touto and came up with a few contingencies: pretend to store the Pandora Box at the abandoned Namba Heavy Industries Research Institute's basement in an attempt to distract Kazumi Sawatari and the Three Hokuto Crows, and to have Ryuga lead a Touto squadron to Hokuto. Before his plan could come to full fruition, however, Gentoku was overruled by his father Taizan Himuro, whom had made a surprise recovery from his coma. Exiled from Touto, Gentoku revealed himself as Night Rogue and attempted to escape with the Pandora Box only to be intercepted by Build, who recovered the Pandora Box as Gentoku only just got away.

Behind the scenes
In Kamen Rider Build, Pandora Box serves as the "" of the series, a plot device often used in many literary narratives.