Kosuke stands as one of Konpei Island's two primary guardians alongside Rikimaru, tasked with protecting the island's last surviving dragon—a duty forged by their shared upbringing in a demanding environment. Both guardians honed practical survival skills through rigorous training and hunting within the island's rustic landscape, cementing their bond to the homeland. His life of simplicity and vigilance grew more critical as Konpei's dragon population dwindled over time, fueling his commitment to preserving the island's ecological and cultural equilibrium against outsiders.

He navigates daily life with pragmatic directness, addressing visitors' needs through unfiltered honesty—such as guiding them to natural facilities while warning of environmental threats like snakes. When external dangers escalate, Kosuke's protective role intensifies. The arrival of a Tokyo professor to study the dragon coincides with an invasion led by militarist Yamada Daihachirou, whose forces aim to steal the gem embedded in the dragon's forehead. Yamada deploys advanced mecha units and mercenaries, including Michael Commando. Kosuke confronts these threats head-on, engaging mechanized adversaries like a mechanical sumo wrestler with his combat expertise. His resilience against technologically superior foes underscores both his adaptability in battle and unwavering dedication as guardian.