Hazard Trigger

The Hazard Trigger (ハザード トリガー) is a turbocharger-like device that allows Kamen Rider Build to upgrade each Best Match into a Super Best Match (スーパベストマッチ).

Design
The Hazard Trigger is composed of the following parts:
 * The Force Ride Meter (フォースライドメーター) is located at the centre of the Hazard Trigger. It measures the fighting ability of the user, and the higher the reading, the more powerful the attacks are. However, if the meter reaches the dangerous zone during battle, the user will go beserk due to massive amounts of stimuli, causing a loss of sense of self.
 * The Progress Tank (プログレスタンク) is the handle sticking out of the Hazard Trigger. It is filled with an enhancement agent named Progress Vapor (プログレスヴェイパー), a reinforcement agent developed from Nebula Gas components, and has the ability to raise Hazard Levels. This agent reacts with Transgel Solid inside of Fullbottles and turns them into metallic components, During transformation, the Progress Vapor is poured through the Hazard Ride Builder (ハザードライドビルダー) and processed into reinforced equipment along with the contents of the Fullbottles, creating the Hazard Suit.
 * The BLD Ride Connector (BLDライドコネクター) is the grey part sticking out of the bottom of the Hazard Trigger. It connects the trigger to the BLD Ride Port (BLDライドポート) top of the Build Driver. Responsible for developing the Hazard Ride Builder.
 * The Security Clear Cover (セキュリティクリアカバー) conceals the BLD Hazard Switch, preventing accidental pressing during battle.
 * The blue button on the Hazard Trigger is known as the BLD Hazard Switch (BLDハザードスイッチ), which is used to activate the switch itself before use. Once transformed, pressing it allows access to Max Hazard Mode and the first turning on vortex crank will bring Build to Overflow (オーバーフロー) Mode, raising the both the Hazard Level again fighting ability, which is potent enough to inflict fear upon both enemy and ally alike. Upon entering Overflow Mode, turning the vortex crank on Build Driver for the second time will allow Build access to his Hazard Finish (ハザードフィニッシュ), a powerful Rider Kick.

Functionality
"Like I thought, they went out of control. Wanna know how you can stop their power? The forbidden item created by Katsuragi... the Hazard Trigger."

- Blood Stalk revealing the Hazard Trigger to Sento

The Hazard Trigger, dubbed the "forbidden item" by its creator Takumi Katsuragi, can massively boost the Hazard Level of its user, with deadly side effects. Attached to the Build Driver, it upgrades Kamen Rider Build's standard two-Fullbottle forms into Hazard Forms, granting him great strength. However, after several minutes in a Hazard Form, Build will lose consciousness and go on a rampage, attacking anything that moves. The Hazard Trigger can be used to permanently upgrade a Smash, but if that Smash is defeated afterwards, they will die.

According to Soichi Isurugi, a user might be able to overcome its side effects if their Hazard Level is high enough. Sento eventually manages to overcome its side effects entirely by creating the FullFull RabbitTank Bottle, upgrading RabbitTank Hazard Form into RabbitRabbit Form and TankTank Form.

To access Hazard Forms, the BLD Hazard Switch is pressed before attaching the Hazard Trigger to the Build Driver above the Vortex Charge. The Build Driver is then used normally, triggering a transformation into a Hazard Form instead of a normal Best Match form. While in a Hazard Form, the Build Driver's Vortex Lever can be cranked again to trigger the Hazard Attack (ハザードアタック) finishing move. If the BLD Hazard Switch is pressed again to trigger Max Hazard mode, the Vortex Lever can be cranked again to activate Overflow (オーバーフロー) Mode, turbocharging Build's strength, and once more to activate the Hazard Finish (ハザードフィニッシュ) attack.

With the Hazard Trigger in Max Hazard Mode, the FullFull RabbitTank Bottle can be inserted into the Build Driver to upgrade RabbitTank Hazard Form into either RabbitRabbit Form or TankTank Form. In these forms, the Hazard Finish is upgraded into the RabbitRabbit Finish (ラビットラビットフィニッシュ) or the TankTank Finish (タンクタンクフィニッシュ).

To permanently upgrade a Smash into a Hazard Smash, the Hazard Trigger is hooked up to a special machine which the subject will lie in to be infused with the Hazard Trigger's power.

Hazard Forms
Kamen Rider=

Two Fullbottles

 * Kamen Rider Build
 * RabbitTank Hazard Form (Build Episodes 20-21, Raising the Hazard Level ~7 Best Matches~: Final Chapter, Build 22-26)
 * SmaphoWolf Hazard Form (Raising the Hazard Level ~7 Best Matches~: First Chapter)
 * HawkGatling Hazard Form (Build Episode 22)
 * KaizokuRessya Hazard Form (Build Episode 24, 35)
 * KeyDragon Hazard Form (Build Episode 35)

FullFull RabbitTank Bottle

 * Kamen Rider Build
 * RabbitRabbit Form (Build Episodes 27-36, 38)
 * TankTank Form (Build Episodes 28-33, 35-36)

Finishers
Overflow Mode=
 * RabbitTank: This finisher has two variations:
 * Build transfers surplus Nebula Gas into his HZ Deadly Gloves and HZ Vanish End Shoes and throws powerful punches and kicks. Additionally, Build also can simply touch the enemy to deliver this finisher.
 * Build rushes at the enemy at maximum speed.
 * SmaphoWolf: Build transfers surplus Nebula Gas into his HZ Deadly Gloves and delivers a powerful punch, summoning a wolf-like energy projection which "bites" down on the enemy.
 * HawkGatling: Build performs a series of blasts with the Hawk Gatlinger while flying around the enemy with the Solstall Wings.
 * KaizokuRessya: Build repeatedly punches the enemy with his HZ Deadly Gloves delivering purple shockwaves on impact.