Once a special forces operative named Dino from an unspecified nation, he now bears the codename B-9 and operates as Shadow. His military service led to involuntary participation in the "B Project," an experiment overseen by scientist Gilria testing a prototype Jack Armor. This ordeal inflicted severe memory loss and ignited an intense drive for vengeance, propelling him to Japan.

Shadow prowls solo, never formally joining the Metal Jack unit. Instead, he intercepts their mission communications using an old police radio, inserting himself uninvited into their operations. His key tool is a distinct Jack Brace, an older model scarred by scratches and missing the team's emblem. Featuring a volume knob, this battered device is his transformation trigger.

Activating the brace transforms him into Shadow Jack, clad in the experimental B-9 Armor. This unique armor originates from Bolter, a security robot capable of converting into the suit. As a military prototype, it carries a critical safety flaw: the armor automatically deactivates after precisely five minutes of use. Both Bolter and the armor deploy formidable weaponry, including a wrist-mounted machine gun, twin 8-tube missile launchers flanking the torso, and dual shoulder cannons.

Haunted by fragmented memories and trauma from the B Project, Shadow relentlessly pursues Gilria for revenge. His unsanctioned interventions in Metal Jack missions define his path, maintaining his lone-wolf vigilante status throughout the series without ever integrating into the team.