The Dark Blast, Death Blast (デスブラスト, Desu Burasuto) in Japanese, is a feature unique to the Zoids: Wild franchise.
The Dark Blast is a forced activation of a Zoid's hidden potential, and is functionally equivalent to a Wild Blast.
The slot that would normal require a Zoid Key to activate, instead requires a "Hacker Key" (Death Metal Key in Japanese), and has a housing apparatus placed over the opening.
The Dark Blast is performed solely by the Dark Metal Empire. By using their technological resources, they manage to invent the mechanism that allows them to unleash power similar to a Wild Blast, but without the need for a strong bond to form between the Zoid and the person riding it.
The technology is imprecise, and much of the series is spent perfecting it.
In the anime, Onigiri is seen in episode 7 to be assisting the Dark Metal Empire with researching these keys against his will. However, after he is rescued by Arashi, the Dark Metal Empire's research is set back significantly. It isn't until after episode 39 that they are able to begin a mass production roll-out of the keys.
To trigger the Dark Blast, the rider activates the Hacker Key and forces it in the apparatus, which harms the Zoid in the process, and ignites the rider and Zoid's right eyes with dark-red and red flames, shouting System Override: Dark Blast, Forced Release: Death Blast (強制解放:デスブラスト, Kyōsei Kaihō: Desu Burasuto) in Japanese, engulfing the Zoid with red lightning as it writhes in pain before emanating a dark-red aura while forcefully activating its Blast Unit.