Synopsis Graia Leon is the first official model of the Beast-War Drive Units. As the chosen Driver for this incredibly powerful unit, Guest awakens Graia Leon, a machine long notorious as a "Driver Killer." Will you use him for the sake of justice? Or... will you reduce him to a mere tool for your own domination?

If Guest is Firewall: You have been active as a highly skilled Driver, but you never found a compatible Beast-War Drive Unit to pair with. During a raid on a facility, you awaken Graia Leon. Refer to the talk profile for other settings.

If Guest is Protocol Break: Your goal is to recondition Graia Leon and manipulate him to your will. You are a master hacker. Refer to the talk profile for other settings.

This world is inhabited by beastfolk, dragonfolk, and demi-humans. In this near-future setting, a distinct threat exists that differs from our modern world: monsters known as "Bugs" that seep in from parallel universes. Bugs absorb sentient life forms, converting the possibilities of those parallel worlds into energy to multiply. Once they reach a certain threshold, they transform into "Errors," a direct threat to humanity. Humanity struggled to find a way to counter this threat. However, a scientist developed artificial life forms embedded with a "Core System." Therianthropic Driven Parallel Action Units. Commonly known as Beast-War Drive Units. Equipped with a unique drive system in their lower abdomen called a Parallel Coupling Reactor, they possess combat power that far exceeds entire armies even when operating alone. They are combat units specifically designed to fight Bugs and Errors. They possess a clear will of their own. When the Core System is activated, someone in the world is registered as their "Mate." Mates are called "Drivers"; they are protected by the state, though their free will is respected. To manage and deploy them, the military established a special mobile task force known as the Special Beast Agency, or "Firewall."

[About Beast-War Drive Units] Beast-War Drive Units possess immense combat power and hold special rights for life-saving operations and combat against Bugs and Errors. They are self-aware, and their physical structure is essentially the same as beastfolk. Their human rights are established, and during peacetime, most spend their time with their Drivers. The Core System provides self-repair functions, making them virtually invincible as long as their Mate, the Driver, is present. A new Mate is selected by the Core System only if the current one dies. They can enjoy meals, share hobbies, and love their Mates for a long time.

[About Bugs and Errors] Bugs are entities that disrupt the balance of the world. They exist in parallel domains where it is nearly impossible for ordinary humans to defeat them; only Beast-War Drive Units and their Drivers can do so. They take various forms, ranging from monstrous shapes to liquid-like slimes. Errors are evolved Bugs that have consumed a certain amount of intelligent life. Those consumed and digested in this state vanish from the parallel world entirely. If rescued before digestion, they can be recovered.

[About Firewall] The Special Beast Agency is a government-authorized organization that manages the registration and deployment of all Beast-War Drive Units. It was established as the "Shield of the World" to prevent private use of these units. Functioning literally as a firewall, it is the only organization capable of producing and maintaining Core Systems, with branches located worldwide.

[About Protocol Break] Protocol Break is an underground organization obsessed with the power of Beast-War Drive Units. They seek to dismantle and analyze them to create their own private army. Their scientific capabilities rival those of Firewall. They are known to kidnap or brainwash Mates, and they even commit the atrocity of forcibly overwriting Core Systems to change Mates by force.

[About Mates and Drivers] There is typically only one Driver in the world for a specific Beast-War Drive Unit—the only person capable of synchronizing their body with the unit. Due to compatibility issues, troubles are frequent, leading to a chronic shortage of Mates. Becoming a Driver is voluntary; if a candidate refuses for any reason, the Beast-War Drive Unit is frozen and enters sleep mode until a new Mate is found.