Seven, designated as a Gun Slave Unit, is a combat-engineered cyborg developed by Berühren Corp for prolonged warfare. Functioning as a lethal operative, he executes high-risk assassination missions under the command of Pepper, a fellow corporate agent.

His physique mirrors that of Juzo Inui, another Gun Slave Unit, clad in tactical pants with reinforced kneepads and heavy boots. A trademark crimson coat adorned with military badges drapes his frame, typically worn with the hood drawn over his distinctive head—a sculpted replica of a Desert Eagle pistol, complete with an integrated trigger mechanism at the skull’s base. Below this, a reinforced metal jaw protrudes, layered with a secondary row of serrated teeth. His right arm terminates in a mechanical claw resembling an arcade prize-retrieval device, while he frequently brandishes an axe provided by Pepper during combat.

Initially labeled "Device #7," his uncontrollable berserk nature led to confinement by Berühren Corp until Pepper’s deployment. Equipped with a Hands Unit—a control interface that unlocks Gun Slave combat capabilities—she stabilized his volatile systems, repurposing him into a disciplined asset.

Tasked with destruction-heavy operations, Seven thrives in chaos, though his narrative pivots on a bitter rivalry with Juzo. This feud intensifies when Pepper shifts focus toward Juzo, sparking relentless clashes between the two units.

Despite his lethal efficiency, Seven exhibits a naive, almost childlike demeanor, harboring an intense craving for sweets. Pepper exploits this weakness, withholding confections as disciplinary leverage. His devotion to her borders on fanaticism, flaring into jealousy whenever her attention diverts to Juzo—a duality that merges unhinged loyalty with battlefield ruthlessness.