Ryou Aguri is a 23-year-old Formula 1 race car driver defined by pride and a reserved nature, maintaining formal distance from strangers but showing rare smiles among trusted friends. He perished shielding Jun Zaizen, heir to the Zaizen Group conglomerate, during an assassination attempt, with police officer Ken Kanzaki and wrestler Gō Gōda present.

His sacrifice earned him a place in the covert "Metal Project" under Tokyo Metropolitan Police commander Masanao Daigo. Resurrected as a cyborg, Aguri operates as Silver Jack within the armored police unit Metal Jack, concealing his cybernetic existence and duties from all personal connections.

In combat, Silver Jack wields a lightsaber-style weapon with lightning speed, leveraging racing-honed reflexes for close-quarters engagements against robotic enemies. This agile approach distinguishes him from Red Jack’s marksmanship and Blue Jack’s brute strength. A peculiar weakness emerged during a mission: he cannot ride a bicycle.

Early struggles with dual-identity pressures led Aguri and Gōda to abandon the Metal Jack unit temporarily during endurance training. Both openly criticized the unit’s secrecy and exhausting demands before Kanzaki convinced them to rejoin.