Mitsukuni Hyuga is the founder and chairman of Hyuga Corporation, a position he earned through a lifetime of dedication to building the company into a major economic success. At age fifty-four, he has spent his entire career pursuing his ambition, which centers on the development and commercialization of artificial muscle fiber technology. His ultimate goal is to complete the Marishi Machina, a powered suit that he believes will secure his company's future in an emerging global market.

As a leader, Mitsukuni is strict and demanding, especially toward his son, Kotaro Hyuga. He raised Kotaro with a focus on discipline and leadership, training him from boyhood to become his successor. This rigorous upbringing culminated in Mitsukuni appointing Kotaro as project leader for the new powered suits, trusting him with a venture on which the company's fortunes rest.

In the story, Mitsukuni serves as a pivotal figure whose decisions drive the central conflict. He is deeply involved in the secrets surrounding the early development of the powered suits, including the disastrous test that resulted in the deaths of Dan Amo's father and the coma of Dan's mother. Mitsukuni deliberately concealed the truth about that incident for years. When journalist Makina Mikage confronts him, he reveals that Dan's mother is still alive in cold sleep, and he suggests that repeating the original test might bring answers. His motives are calculating: he uses the hope of reviving Dan's mother and uncovering Makina's father's intentions as leverage to advance his own agenda.

Mitsukuni's key relationships are defined by his purpose. With Kotaro, he is a demanding father who grooms his son for leadership but also puts immense pressure on him. With Dan and Makina, he is an antagonist whose past actions have entangled their lives, yet he offers them a path forward that serves his interests. The epilogue finds him waiting for Dan and Makina with an unsettling expression, signaling that his ambitions remain unresolved even after the main events have concluded.

Development-wise, Mitsukuni does not undergo a personal transformation. Instead, he remains a fixed point of authority and ambition around which other characters grow. His notable ability is not physical but strategic: he is a shrewd corporate leader who built his company from nothing, possesses deep technical knowledge of the powered suit technology, and is willing to sacrifice transparency and personal relationships to achieve his vision. His role is that of a catalyst who sets the story's events in motion and continues to exert influence from behind the scenes.