Gaz Kewick (alternately spelled Guz Kyuick or Cuicc) acts as a primary antagonist commanding MIX, a private military company and security firm masking illicit operations with legitimate fronts. MIX wields substantial international influence through arms dealing and weapons sales to global defense departments.

Kewick pioneers a dangerous technological innovation by transforming precious diamonds into concealed explosives, filling them with nitroglycerin to create highly volatile bombs. This weaponization of gemstones forms the core of his strategic warfare and criminal enterprises.

Despite projecting ruthless business acumen, Kewick maintains a familial identity as Michelle’s father. He cites financial security for his wife and daughter as his initial motivation for founding MIX. Yet his obsession with expanding the company’s power consistently overrides family commitments, culminating in his absence from his wife’s funeral due to business priorities.

This neglect forged a profound rift with Michelle, who views his ventures as morally corrupt and actively opposes them—including hiring external agents to sabotage his diamond-weapon schemes. Kewick’s failure to align his professed familial devotion with his actions underscores a deep personal contradiction.

Within the narrative, Kewick’s diamond-weapon system (NDW system) directly ignites converging plotlines. His connections draw mercenary associate Ryatt into conflict, pulling Jigen into temporary opposition against Lupin. Simultaneously, his possession of the "Goddess’s Teardrop" diamond makes him a target for both Lupin (contracted by Michelle) and Fujiko Mine (who recruits Goemon). Kewick thus pivots the intersecting missions of central characters.

As MIX’s leader, he directly confronts protagonists, deploying technological innovations and vast resources. These clashes typically conclude with his weaponized-diamond plots foiled and his neglectful priorities exposed.