Build Driver

The Build Driver (ビルドドライバー) is the transformation device used by both Kamen Rider Build and Kamen Rider Cross-Z. As the Rider System (ライダーシステム) created by Takumi Katsuragi, it uses Fullbottles as its primary collectible device. Sento later made another Build Driver for Ryuga to use to become Cross-Z after the first time he used Sento's Driver.

According to Sento Kiryu, one must have a Hazard Level of 3 to be able to transform using the Build Driver. Otherwise, they'll get electrified and rendered unconscious by the anti-theft system on the belt.

As stated by Sento and later seen in the flashback of his first battle, the Build Driver didn't originally announce Best Matches until he'd modified it to do so.

The Build Driver is later revealed to be a a safer and weaker version of the Evol-Driver, due to Takumi Katsuragi being aware that the Evol-Driver could not be used by a normal human.

Transformation
Kamen Rider Build transforms by inserting two Fullbottles into the Build Driver's Building Modules (ビルディングモジュール) and plugging them into the Twin Fullbottle Slots (ツインフルボトルスロット). The user then turns the Vortex Lever (ボルテックレバー), a crank that generates power to the Vortex Charge (ボルテックチャージャー) energy core generator unit by turning the lever. This gives the Nitro Dynamo (ニトロダイナモ) inside the Vortex Charge the momentum it needs to generate power for transformation and finishers. Larger amounts of energy can be generated by increasing the momentum of turning the Vortex Lever and rotation speed of the Vortex Charge.

In a rare instance for Rider Belts, in Episode 1, the inner workings of the Build Driver were seen during transformation. As the Vortex Lever and Vortex Charge turns, it moves the gears and pistons inside the belt which pump essence from the Fullbottles out of their containers through pneumatic tubes, which move out of the belt and form the base for assembly of the suit. If the user is transforming into a Best Match form, the Driver then initializes the Snap Ride Builder (スナップライドビルダー) after the essences have hardened into the Halfbodies, snapping the two parts together and completing the transformation. The Snap Ride Builder will not appear if the user is moving during the transformation, while in some instances, the pneumatic tubes of the Snap Rider Builder will simply appear in a quick flash so as to speed up the transformation.

The Build Driver is layered in an alloy called the Safety Guard Case (セーフティガードケース), designed to resist high temperatures, high impacts of force and attacks by the Smash. As a security feature, the belt uses the Qualifizer (クオリファイザー) fastener to do a biometric scan of its wearer to determine if the intended user has a Hazard Level of 3. If it is not, the belt will not function and go into a protective shutdown state, punishing the would be wearer. If the user does, the belt will continue to operate normally.

An ideal combination of two matching Fullbottles will create a Best Match (ベストマッチ) form, but any other imperfect combination is known as a Trial Form (トライアルフォーム).

Kamen Rider Cross-Z transforms by inserting the Dragon Fullbottle into the Cross-Z Dragon, before inserting it into the Build Driver, and turning the crank.

When transforming into Cross-Z Magma by inserting the Dragon Magma Fullbottle into the Cross-Z Magma Knuckle before inserting it into the Build Driver and turning the crank, the Magma Ride Builder (マグマライドビルダー) is summoned and pours Variable Magma over the rider. This substance forms a casting of the Cross-Z Magma armor as numerous smoldering dragons rise up from the pool of lava. Once cooled and hardened, the Magma Ride Builder shatters the cast, releasing Cross-Z Magma.

Finishers
While transformed, Build/Cross-Z initiates a finishing move by turning the Vortex Lever. Build's Best Matches use the Vortex Finish (ボルテックフィニッシュ), and Build's Trial Forms use the Vortex Attack (ボルテックアタック). Cross-Z' finisher is the Dragonic Finish (ドラゴニックフィニッシュ).

Snap Ride Builders
Transformation Setups=

Portrayal
The voice of the Build Driver was provided by KORBY.