13 years ago astronauts through the advancement of technology finally made it to Mars, a planet deemed to be filled with alien life, only to find nothing but ruins of a civilization carved in sandy stone.  It looked like the attacks were recent, yet also looked as if it had been centuries since then with the astronauts beginning their exploration of the planet. The crew split into two 2 man groups, each going in an opposite direction, the ones who'd find something reporting in only an hour later. As the rest of the crew made their way over they found a large sort of igloo, it was made of something that looked valuable as it sat in a large sunken crater. The 2 who didn't find this would make the first move, carefully making their way down as they walked up to the large opening, surprise escaping their lips as they peered inside. It, although should've been dark, was lit up which raised caution as they continued forward. After several minutes of searching, they'd found a strange box in the center of the room, located on a pedestal in what almost looked like a glass box. Lifting it the astronauts would take this found treasure back to Earth.

 Back on earth, the Pandora's Box was immediately pushed into the labs of Faust, which at the time happened to be one of the many companies that dealt with military warfare and advancements in evolution through science. Faust while overlooking the project stumbled upon many different things to note from this strange box, a scientist of Faust beginning to work on a project to build tools of defense utilizing the Pandora Box's research. The Pandora Box also emanated a gas that was harmful to animals and humans alike, an exposure to the gas in testing had proved that you could easily get a high fever just by barely breathing it in. But as the box was moved out of Faust's hands and into the care of the Government's scientists Faust still had kept samples of this gas to mass produce and try to utilize it, only ending up creating monsters. Faust over the span of 6 years effectively found a way to utilize its effects through the Transteam Gun rider system, created by a scientist by the name of Yuuto Sukabe and perfected and finalized by another scientist not named.

Utilizing the blueprints Yuuto Sukabe made, along with the research data, they would find that exposing humans to the gas for long enough could create monsters. Monsters that made their own form of nebula gas throughout their bodies, and was the perfect opportunity for  Faust to create the 'Fullbottles'. Yuuto Sukabe would've left the Faust Labs a year after, though with it taking a prototype driver he had in mind along with a handful of fullbottles. One of the many users of the Transteam Gun named Bloodstalk took note of this, wishing to utilize their genius still as they tracked the man down. Proposing a deal with Yuuto Sukabe the man would refuse, causing Bloodstalk to get upset, erasing their memories aside from their genius, and changing their appearance as he decided it best to bend them to his will one way or another, either that or it was just to have fun.

After these events Yuuto Sukabe was presumed dead that day, found by a stranger in his apartment, one that'd immediately be accused of murder. This story differing from the show after that point, as it could've been anyone that was there that day, not having to be Cross-Z. Eventually, this led to Bloodstalk leaving him in the hands of an establishment, as an owner stand in or just leaving him somewhere with the tools he needed was anyone's guess. 

Now the amnesiac must choose, will they battle and defend against the smashes? Will Cross-Z be trans? Will Evol ever kiss Build!? Find out all this and more in the next episode of Kamen Build Z!