Kyoko Matoba is a young girl who becomes an ally of Kotaro Minami during his battle against the Crisis Empire. She first appears as a middle school student whose life is shattered when her parents are murdered by the Crisis monster Mundayganday. This traumatic event serves as the catalyst for her entire involvement in the story, as she is driven by a powerful desire for revenge against the Empire that took her family from her.

In terms of personality, Kyoko is characterized as a quiet and reserved individual, but beneath this calm exterior lies a remarkably strong and determined heart. Her resolve to avenge her parents is unwavering, pushing her to pursue extraordinary means to gain the power she needs. She is courageous and willing to take bold actions, such as infiltrating Crisis units as a spy or attacking enemy hideouts on her own. Her determination is so fierce that even when she initially has no special abilities, she insists on confronting her parents' killer. This inner strength earns her a place as a trusted comrade, and the main protagonist, Kotaro Minami, accepts her as a fellow warrior without question or patronizing dismissal.

Kyoko's central motivation is the avenging of her parents, which fuels her intense training to develop extraordinary abilities. She does not have her powers at the outset but actively strives to cultivate them through sheer force of will. As she trains, her desire for power grows, leading her to pray to her deceased father for the strength to fight. This dedication allows her to become a formidable fighter in her own right.

Throughout the story, Kyoko serves as a supporting ally to Kamen Rider BLACK RX. Her primary role is to assist in the fight against the Crisis Empire using her unique powers and combat skills. Her abilities include telekinesis, which she develops after rigorous special training. Initially, she shows the potential to control elements of nature such as plants and rocks, but her focus eventually sharpens into the specific ability to manipulate groundwater. She can also create water from nothing and use it to help others, as demonstrated when she provides water to desperate citizens during a Crisis-engineered shortage. Her water abilities require significant stamina, and overusing them greatly consumes her energy. In addition to her ESP powers, Kyoko is also skilled with a bow and arrow, showing confidence in her archery abilities during later battles.

Regarding key relationships, Kyoko fights alongside Kotaro Minami, who encourages her training and accepts her as a comrade. She also develops a bond with Reiko Shiratori, another key female ally, and the two of them join Kotaro's fight together. Her relationship with her deceased parents is the emotional core of her character, as her quest for revenge is rooted in her love for them and her inability to accept their loss. She also forms a connection with the Sahara siblings, as after the Crisis Empire is destroyed, she lives together with them, having also lost her parents. Additionally, she is noted to have a connection with Shiro Kazami, a veteran hero she co-battles alongside.

Kyoko experiences notable development from an ordinary, grieving girl into a powerful esper and skilled warrior. Her journey is one of transformation driven by tragedy and determination. She begins with no powers but, through focused training and an unbreakable will, she successfully awakens her ESP abilities. By the end of her training, she gains the confidence and skill to actively participate in battles as a warrior, even saving Kamen Rider RX from a difficult situation with her archery. Her development arc concludes with her finding a new family with the Sahara siblings after the destruction of the Crisis Empire, suggesting a move from revenge to rebuilding her life.