Daisaburō Higashiyama is introduced as an ordinary high school student whose life changes dramatically when he inherits a legacy connected to an ancient robotic entity. This inheritance follows the death of his father, a scientist who discovered a buried mecha while pursuing extraterrestrial technology during an expedition. Reluctant and unprepared, Daisaburō is thrust into the role of the entity's pilot when hostile alien powers emerge and threaten Earth's survival.

His personality is initially marked by significant self-doubt and the crushing weight of sudden responsibility. He is reluctant to accept his role and feels unready for the challenges he faces. These early feelings of insecurity and hesitation clash with the escalating battles he is forced into, an experience that gradually forges his determination. As he confronts these trials, his character shifts from a hesitant defender to a proactive guardian who prioritizes unity and trusts in his allies.

Daisaburō's primary motivation stems from the bonds he forms with family members connected to the mecha's origins, which anchor his resolve to protect others. His understanding of the conflict deepens through fragmentary flashbacks and the rediscovered research notes left by his father, which reveal secrets about the entity's latent abilities and the true motives of the alien invaders. Furthermore, his alliances with military operative forces and fellow pilots challenge his perceptions and teach him the harsh realities of leadership and sacrifice.

His role in the story is that of the reluctant pilot who must rise to the occasion, evolving under pressure. Key relationships include his ties to his family, whose legacy is intertwined with the mecha, and his comrades within the military and among other pilots. These alliances are crucial in shaping his worldview and decisions. Daisaburō undergoes significant development, as loss and moral dilemmas in the heat of war force him to confront the human cost of the conflict. Crucial decisions made under pressure mark his transition, and each battle strips away his insecurities, culminating in a transformation from a resistant teenager to a determined protector who learns to balance fragile humanity with the relentless pull of fate. His growing strategic mastery and the developing power of the mecha directly reflect his inner confidence, honed through trial and combat, representing his most notable abilities.