Evolt

"I'm the game maker. I derive the best strategy by considering every possibility. Everything is going as planned."

- Blood Stalk's speech to Night Rogue

Blood Stalk is one of the leaders of the organization Faust and the primary antagonist of Kamen Rider Build.

His true identity is revealed to be Evolt, a mysterious entity who annihilated the ancient civilization on Mars long ago using the power of the Pandora Box. He took over the body of Soichi Isurugi, owner of the cafe nascita and secretly the astronaut who discovered the Pandora Box 10 years ago. Therefore, Blood Stalk is the primary antagonist of Kamen Rider Build that starts the whole series' event, being responsible for the Skywall Disaster that separated Japan.

As Soichi, Blood Stalk is portrayed by Yasuyuki Maekawa. The voice role of Evolt's true voice is provided by Tetsuo Kanao.

Past
Not much known about Evolt's life on Mars, but it is heavily implied by Vernage, the Queen of Mars, that Evolt was the one who used Pandora Box and annihilated Mars civilization.

Ten years prior to the events of Build, Soichi Isurugi, an astronaut working with the Kiwami Project, discovered the Pandora Box while on Mars. Soichi released Evolt and was possessed by him. At the ceremony back on Earth, under Evolt's control, Isurugi applied his hand to the Pandora Box, causing the Sky Wall Disaster.

"Soichi" was later arrested and placed in a mental hospital, along with his daughter, Misora Isurugi who was also exposed to the box and gained the ability to purify Fullbottles.

However, "Soichi" escaped about a month later. Seven years later, he was appointed as a special consultant for the Pandora Box. He also co-founded Faust with Gentoku Himuro.

Under Faust
Misora later joined Faust to purify the Fullbottles for them, though she was unware at first of their true purposes. When she eventually found out about Faust's intentions, she lost her will to continue working for them. "Soichi" then "saved" her and took her back to the cafe, where he convinced her to continue purifying the bottles for good.

"Soichi" later stole the Pandora Box panels from the Touto Institute of Advanced Matter Physics to ensure their confidence and plastered into one of nascita's basement walls. He also took along a Build Driver and some Fullbottles from faustl.

Dealing with Katsuragi
When Takumi Katsuragi attempted to quit Faust, Blood Stalk knocked him out and switched his clothes and face with Taro Satou, whom Stalk had previously killed by Stalk. Stalk then left Taro Satou in the alleyway and erased Takumi's memories before talking him back to Faust to experiment on him. On September 5th, Isurugi brought the amnesiac Katsuragi to a small alleywayi After Takumi woke up, Soichi renamed him Sento Kiryu and nurtured him into Kamen Rider Build so that, with Build fighting more monsters, Soichi would have reasons to have Misora purify more bottles.

Betrayal of Night Rogue
After Gentoku refused to reveal the location of the Pandora Box due to Stalk's treachery, Stalk began searching for the box on his own, eventually tracking it to the Namba Heavy Industries Integrated Science Laboratory. Stalk skirmished with both Sento and Ryuga and Night Rogue before teleporting away with the Box.

After Gentoku disbanded Faust to cover his tracks, he discovered that Juzaburo Namba had dropped Gentoku as a partner and instead partnered up with Blood Stalk.

His true identity was eventually discovered by Build and Ryuga after they defeated him in a fight and cancelled his transformation. His cover blown, Isurugi revealed to the two that Gentoku was Night Rogue and allowed them to keep the Green Panels and the Pandora Box.

Rebuilding Faust
Blood Stalk later rebuilt Faust within Hokuto and temporarily aligned with them, providing them with the resources they needed to create Kamen Riders. However, he later switched over to working with Seito when they invaded and conquered Hokuto due to most of Hokuto's forces being involved in the war with Touto.

After Seito lost a proxy battle with Touto and thus had to relinquish the Fullbottles and Pandora Box as per their agreement, Blood Stalk was summoned by Namba to kill Seito's Prime Minister Masakuni Mido and swap their faces so Namba could take control of Seito.