Kazuya Taki is an FBI agent who appears as a key ally to the Kamen Riders. He is an American citizen of Japanese descent, and his initial assignment was to investigate the activities of the terrorist organization Shocker in Japan. Before his career as an agent, he worked as a professional motorcycle racer, a skill that would prove invaluable in his fight against evil.

Personality wise, Taki is portrayed as a friendly, easygoing, and courageous individual with a strong sense of justice. Despite his amicable nature, he is highly capable and maintains the calm, collected demeanor of a trained federal agent in serious situations. He possesses a particularly soft spot for children, often acting as a protective older brother figure and showing great concern for their well-being. While generally clever, he can sometimes act impulsively, particularly when angered, and has a tendency to leap into danger without fully considering the risks, driven by a fierce sense of right and wrong.

Taki’s primary motivation for joining the fight against Shocker is personal. He was on his honeymoon when he was attacked by the monster Gebacondor, and his wife was injured in the incident. Seeking revenge and justice, he began assisting the Kamen Riders. As an FBI agent, his mission to dismantle Shocker aligns with this personal vendetta, driving him to become one of the Riders' most dedicated human supporters.

In the story, Kazuya Taki serves as a vital human ally to the original Kamen Riders, Takeshi Hongo (Kamen Rider 1) and Hayato Ichimonji (Kamen Rider 2). He first appears as a rival motorcycle racer before revealing his true identity as an agent. His role often involves infiltrating Shocker bases in disguise, rescuing captured friends, and providing support in battle. In the film Kamen Rider tai Jigoku Taishi, he and Kamen Rider 1 must fake their deaths to infiltrate a Shocker base and stop Ambassador Hell from using a super destruction light beam to destroy Tokyo. He frequently acts as a field operative, using his espionage training to gather intelligence on the enemy.

His key relationships are with the two Kamen Riders, whom he befriends and trusts implicitly, as well as with Tobei Tachibana and the members of the Tachibana Racing Club. He forms a particularly strong bond with the children in the Rider club, treating them like younger siblings.

Regarding character development, in later manga continuations such as Kamen Rider Spirits, Taki takes on a more prominent role. After the destruction of Shocker, he returns to the FBI, though few believe his stories about the cyborg terrorist group. When monster activity resurfaces in New York City, he adopts a costumed persona known as Taki Rider, donning a black suit and skull-themed helmet to fight in the absence of the real Kamen Riders. This demonstrates his unwavering commitment to protecting the innocent, even without superhuman powers. He later becomes the captain of a military support unit called Spirits, which provides tactical and logistical assistance to the Kamen Riders.

Although he is an ordinary human and not a cyborg, Kazuya Taki possesses remarkable abilities. He is an extremely skilled martial artist, proficient enough to defeat multiple Shocker Combatmen with ease and hold his own against lower-level monsters in hand-to-hand combat. His athleticism is borderline superhuman, allowing him to perform feats such as leaping high fences and executing powerful kick-based attacks. He is also a master of disguise and espionage, a natural consequence of his FBI training. His motorcycle riding skills are legendary, rivaling even those of Takeshi Hongo before Hongo became a cyborg. In the Kamen Rider Spirits manga, he uses specialized equipment, such as shotgun-shell-loaded combat boots and gloves to enhance his Rider Punch and Rider Kick, as well as a gun-sword hybrid weapon.