Yoshimitsu Suguro, nicknamed "Bill," is a scientist for Japan's Kanto Army during World War II. His core mission involves researching and reverse-engineering alien technology from extraterrestrial invaders, specifically targeting the control mechanisms of giant Geo-Armor Robots. Collaborating with Nazi scientist Hans Liengel, he works to develop deployable robotic units for military use.

Suguro plays a central role in pursuing a mysterious black attaché case held by protagonist Taishi—inherited from Professor Tokamura—which contains a critical control device for operating one giant robot. He represents the Kanto Army's scientific interests against competing factions including Axis forces and alien entities, all seeking the device. Despite repeated failures to replicate the alien technology, he demonstrates unwavering dedication to securing and reverse-engineering it.

Operating amid espionage, military operations, and factional rivalries, Suguro leverages his scientific expertise to advance the Kanto Army's strategic goal: harnessing extraterrestrial power through the giant robots.