Kiyotsugu Gowa is the second son of Daizaburo Gowa, the head of the powerful Gowa family, placing him within a prominent and politically connected Japanese dynasty. As a member of this family, his siblings include his elder brother Kazukiyo, his younger brothers Kiyoharu and Yushiro, and his younger sister Misuzu. He is established as a man of science and an accomplished researcher, serving as the genius behind the development of the series' Tactical Armor mecha, which he considers his life's work. He plays a key technical role within the family's corporate and military endeavors, often translating and explaining complex test data from the Tactical Armor simulations to his father, Daizaburo.

In terms of personality, Kiyotsugu is initially presented as an aloof and focused individual whose primary motivation is the advancement of his research. His dedication to science and the pursuit of knowledge for its own sake is a core driving force, leading him to cooperate with his elder brother Kazukiyo's elaborate and morally questionable schemes, seemingly willing to disregard potential dangers to his relatives and colleagues in order to further his studies. However, he is not without a personal moral code. While he follows Kazukiyo's plans to a certain extent, he consistently refuses to cross specific ethical lines. For instance, he objects to Kazukiyo's most extreme and cruel experiments, such as forcing soldiers to pilot mecha for thirty-six hours straight using a dangerous psychoactive serum and using his own sister, Misuzu, as a test subject due to her special powers. Furthermore, upon discovering that the mysterious girl Miharu is a Kai, he deliberately chooses to withhold this information from Kazukiyo, stating that there is no telling what his brother might do with it, revealing a protective instinct that contrasts with his earlier apparent amorality.

His role in the story is primarily that of the technical expert and researcher for the Gowa family. He is present during the military exercises testing the Tactical Armors and the private mystical ceremonies attempting to open a singularity, observing and analyzing the results from a scientific perspective. While he lacks the overt ambition for political power that drives his elder brother Kazukiyo, his research is instrumental in the family's larger plans, which seek to harness ancient mystical forces for modern military and political supremacy. His key relationships are defined by his position in the family hierarchy. He works under the direction of his father and elder brother but maintains a separate moral compass from Kazukiyo's ruthless ambition, creating a tension between scientific pursuit and ethical responsibility. He also shows more concern for his younger half-brother Yushiro than Kazukiyo does, with his brother Kiyoharu perhaps showing the most open concern among the older siblings.

Throughout the narrative, Kiyotsugu demonstrates notable character development, subverting the initial expectation of a completely amoral mad scientist. He evolves from a seemingly detached researcher complicit in dangerous plans to a figure who actively chooses to protect others from his family's darker ambitions, such as concealing Miharu's nature and voicing objections to Kazukiyo's most inhumane actions. His notable abilities lie not in combat or politics, but in his exceptional scientific and technical expertise. He is the mastermind behind the development of the Gowa family's advanced Tactical Armor units, and his analytical skills are crucial for interpreting the data derived from both technological and mystical experiments.