Fujisaki Duke is a supporting character in the Megaton Musashi series who serves as the chief mechanic and a lead scientist within the shelter city of Ixia. His primary responsibility is the research, development, construction, and maintenance of the humanoid fighting machines known as Rogues, which are used to combat an alien threat. He is specifically in charge of the engineering division where these advanced combat units are developed, and he is recognized as a skilled and accomplished scientist in his field.

In terms of his role in the story, Fujisaki is instrumental in the creation and support of the special Megaton-class Rogues. His technical expertise is highlighted by his invention of a new twin-drive propulsion system. This innovative system, unlike standard units, requires two pilots to operate in sync, each controlling an individual engine. This system was implemented into the Maximus, a red and bronze Megaton-class Rogue. Beyond its initial development, Fujisaki is responsible for the ongoing repair and upgrading of these critical war machines. For instance, after the Maximus sustained severe damage during the launch of the Ixia, he oversaw its repair and subsequent enhancement into the more powerful Maximus Blaze model, working alongside a colleague named Takumi Kindaichi.

Regarding his personality and motivations, Fujisaki possesses a focused, technical, and innovative mindset, dedicated to pushing the boundaries of engineering to support the pilots on the front lines. His actions consistently demonstrate a commitment to his work, whether he is designing a novel drive system, repairing extensive battle damage, or planning further upgrades to give his team a strategic advantage. He maintains key professional relationships with other members of Ixia's technical staff, such as Takumi Kindaichi, and his work directly impacts the pilots who use his machines, including Jun Kirishima and Momoka Saotome, who were chosen to pilot the twin-drive Maximus. His character development is shown through the evolution of his projects, moving from the initial creation of the Maximus to its repair and successful upgrade into the Maximus Blaze, reflecting his ability to adapt and improve his technology in response to the challenges of the ongoing conflict. Fujisaki Duke's notable abilities lie entirely in his exceptional engineering and scientific expertise, specifically his proficiency in Rogue design, the development of advanced drive systems, and the practical application of mechanical repairs and upgrades.