Hyakume is a demon, or akuma, who serves as a member of the twelve apostles, the loyal companions to the protagonist Shingo Umoregi. In this iteration, Hyakume is depicted as the last survivor of his entire race, though the circumstances leading to this status remain unknown. Physically, Hyakume is a humanoid figure with green skin and a small, pointed nose. His most distinctive and defining characteristic is the multiple eyeballs that cover his body and face, a feature that gives him his name, which means hundred eyes. The skin on areas like his stomach and arms is notably baggy and loose, and he has two floppy ears. In terms of stature, he is approximately the same height as Shingo and his fellow apostle, Mephisto II.

Unlike more villainous portrayals of similar creatures in other folklore-based series, the Hyakume in the 1989 Akuma-kun anime is presented as a peaceful and friendly character. His personality reflects a gentle nature, and he integrates into the group around Shingo without malice. His background is rooted in mystery as a lone survivor, but his role in the story is clear and supportive. Hyakume is one of the key allies Shingo recruits to help battle wicked demons that threaten humanity and to work toward a world where humans and demons can coexist peacefully. They first encounter each other when Hyakume, disguised as a human, is spotted looking at a television from outside a shop window. When a crowd begins to gather around him, he uses his powers to emit a blinding light to escape the unwanted attention. Shingo recognizes him for what he truly is and invites him to his home, an offer Hyakume readily accepts.

As one of the twelve apostles, Hyakume shares a strong bond of loyalty with Shingo Umoregi and his other demon companions, including the powerful Mephisto II. He is a trusted member of the team, fighting alongside them against common enemies. Hyakume possesses several notable abilities that stem directly from his unique physiology. He has the power to remove the eyeballs from his body and control their movement, sending them flying in any direction. This ability can be used to swarm and overwhelm opponents in battle. Furthermore, he can emit a powerful, blinding beam of light from his eyes, which can temporarily stun those who look at him, providing a strategic advantage in both combat and evasion. Throughout the story, Hyakume develops from a solitary survivor of his species into an integral and valued member of a found family, committed to a cause greater than himself.