Masanao Daigo initiates and commands the Metal Project, a covert Tokyo Metropolitan Police Department initiative combating escalating high-tech crimes in futuristic Tokyo City. He selects candidates for cybernetic augmentation based on demonstrated courage, specifically recruiting Ken Kanzaki, Ryo Aguri, and Go Goda after they sustain mortal injuries protecting Jun Zaizen from an assassination attempt by Id. Following their resurrection as cyborgs, Daigo oversees their transformation into the armored police unit Metal Jack and imposes strict secrecy regarding their identities, forbidding disclosure to friends, family, or colleagues.

As operational leader, Daigo directs missions against Id and other threats, utilizing advanced technology including Jack Suits and Jack Armors. He coordinates field operations and training regimens, including endurance exercises designed to enhance the team's effectiveness. During critical developments like Ken Kanzaki's second near-fatal injury, Daigo authorizes the Hyper Project, a medical initiative spearheaded by scientist Ginren Han to further augment Ken's capabilities through cellular reconstruction and enhanced cybernetics.

Daigo maintains ongoing involvement in the unit's strategic decisions, particularly concerning Id's evolving tactics and leadership changes such as Grunwald de Gilria's takeover after Megadeth's demise. His command extends to managing ancillary assets like the cybernetic police dog Lander and the aerial vehicle Jack Chaser.