Pandora Box

The Pandora Box (パンドラボックス) is an extraterrestrial artifact of unknown origin that was found during a manned Mars mission ten years prior to the events of the Kamen Rider Build series.

After it was brought back to Earth for study, it somehow activated and created a "Skywall" that divided the nation of Japan into three separate districts and spawned unidentified organisms later known by humans as the Smash which terrorized and attacked the populace.

No further information has been given about this artifact at this time, including its further significance to the story of the series.