Kido is a mamodo child who takes the form of a lanky, almost puppet-like figure, with large blue eyes and a distinctive horn hidden beneath his top hat. His appearance is completed by a blue jumpsuit marked with a large letter K. Part of his unique nature is that he is partly robotic, a trait that directly influences the machinery-based spells he can cast. Despite his mechanical components, Kido possesses a very expressive and childlike personality. He is often portrayed as cocky and boastful, but this bravado is tempered by a deep-seated gullibility. He frequently falls for the elaborate lies and riddles told by his book keeper, Dr. Riddles, reacting with comical shock each time he learns he has been tricked. He is also easily frightened in dangerous situations, though he consistently overcomes this fear to fight alongside his partner.

Kido's primary motivation throughout the story is his loyalty and admiration for Dr. Riddles. He sees the doctor not just as a partner in the mamodo battle, but as a king and a father figure. This powerful bond gives him the courage to face powerful enemies, even to the point of sacrificing himself to protect his partner and their allies. His role in the story is that of a recurring ally to the main protagonists, often providing support in major battles and serving as a testament to the strength of the partnership between a mamodo and a human.

The relationship between Kido and Dr. Riddles is the central pillar of his character. Their dynamic resembles that of a father and son. Dr. Riddles, a brilliant but reclusive old man with a vast knowledge of the world, found new purpose in life when Kido arrived at his secluded library. Kido's trust and enthusiasm helped the doctor overcome a tragic past as a surgeon who lost a young patient, giving him a reason to apply his wisdom once more. In turn, Kido benefits from Dr. Riddles strategic mind and deep care. The team often uses a battle strategy where Kido withstands initial attacks to create distance, allowing him to unleash powerful long-range spells. In the final arc of the story, even after his own book is burned and he is forced to return to the mamodo world, Kido briefly reappears to aid Zatch in the decisive battle against the ultimate enemy, using his strongest spell to destroy crucial fragments of the opponent and urging Zatch to stay focused.

Kido's abilities all center on his robotic body and machinery. His spells allow him to morph his body parts into various weapons and tools. He can generate powerful cannons from his mouth or chest to fire potent laser beams, as seen in spells like Zegar and Gigano Zegar. His limbs can transform into rocket punches for long-range physical strikes, machine guns for rapid-fire attacks, or separate entirely from his body to evade attacks. He can also create a small army of aggressive miniature copies of himself from a staircase emerging from his mouth. As he grows stronger through the series, he gains access to more powerful spells, culminating in the immensely powerful Mikor Ma Zegaruga, which manifests a giant, divine mechanical entity to attack his foes.