Kamen Rider Blade

Ace Form

Jack Form

King Form

At the age of 11, Kenzaki was orphaned when his family died in a freak fire accident. The powerlessness he felt would forever serve as the motivation to try and protect the defenseless, subsequently leading to being scouted by BOARD. Because of his intelligence and exceptional survival tactics, he would eventually be promoted to field operative and the designated user of Rider System-02. However, during assessment for the Rider System, Kenzaki displayed unusually high fusion coefficiency. Though this caused no immediate concern, as his levels maintained steady intervals. After being promoted to Rider status, Kenzaki would be paired with fellow BOARD Rider and senior operative Sakuya Tachibana in hunting down three Undead within a period of two months.

After sealing the Bat Undead, Kenzaki meets a web-journalist investigating the Rider named Kotarō Shirai who witnessed Kenzaki changing back from Rider form. To lessen the risk of exposure, and to find a place to board after losing his apartment for not paying his rent in time, Kenzaki made a deal with Kotarō: In exchange for information concerning the Riders, Kotarō would provide a place for Kenzaki to stay; being that his salary with BOARD was barely enough to make a living. But later that evening, disaster struck as BOARD HQ fell under attack from the Locust Undead. With Tachibana walking off without offering aid and Karasuma, BOARD's president, no where to be found, Kenzaki and Shiori, one of BOARD's surviving members, set-up a new base of operations in Kotarō's home, using whatever equipment left undamaged during the Undead Raid on BOARD HQ. Though operating at a limit capacity, Kenzaki, Hirose, and Kotarō successful began tracking and sealing any active Undead in the area. But when Kenzaki starts tracking down his renegade partner Tachibana, he encounters Chalice and tries to befriend him after learning of his human identity Hajime.

Kenzaki was later kidnapped by men working for Isaka to be used in an experiment to test the human/Category Ace fusion ratio by pitting him against the Trilobite Undead, his fusion rate increasing upon seeing Hajime with his captors before Chalice gets involved as well before Garren provides backup. But while Isaka starts to manipulate After that Kenzaki learns that Hajime is an Undead, confronting him before they fight until the Zebra Undead start his attack. Though he knew that Chalice was an Undead operating under the alias "Hajime Aikawa", Kenzaki started to believe that there's some good in Hajime and that he's not the monster he originally thought him to be. As a result, eventually learning of Hajime's true nature as the joker, Kenzaki does everything in his power to keep him from reverting to his true form.

However, once the Giraffa Undead was sealed, Hajime begins to lose control and his impulse as Joker comes forth with the Stone of Sealing creating an army of DarkRoaches to eliminate all humans. In the end, Kamen Rider Blade is the only one to combat him head on, both equal in power, intend on saving the Earth and Hajime from himself.

In the series ending, Kenzaki sacrificed his humanity in order to save Hajime, thus becoming the Navy Joker. Hajime is allowed to keep his Human Spirit card to maintain his disguise and stays with the Kurihara family for the rest of his life; but still remembers what Kenzaki has done for him, and if he and Kenzaki cross paths again, fate will step in and force them to fight. Kenzaki departed to ensure this would never happen. The series' final scene shows Hajime walking in a park when he suddenly sees Kenzaki's smiling figure seated on a bench. When he relievedly approaches, Kenzaki's figure vanishes like an illusion.