Mitsuba Shimamura is a central character in the anime adaptation of Tojima Wants to Be a Kamen Rider. He is a 27-year-old human who works as the manager of a family restaurant. His worldview was permanently shaped during childhood when he and his older brother, Ichiyo Shimamura, witnessed actual members of the villainous organization Shocker. This traumatic experience left Mitsuba with the unshakable conviction that Shocker operatives are real and operating in secret, hidden among ordinary people. This belief drives much of his behavior throughout the story.

Mitsuba is warm, socially responsible, and proactive, often taking the initiative to engage with others who appear to share his understanding of the hidden world. When the protagonist, Tanzaburo Tojima, dons a Kamen Rider mask and enters Mitsuba’s restaurant alongside Yuriko Okada in a Tackle costume, Mitsuba immediately approaches them, assuming they are fellow true believers. His dedication extends to his work and his personal passions, particularly his intense fascination with the character Riderman—a figure that becomes central to his identity.

He is trained in aikido, which serves as his primary method of self-defense and complements his eventual role as a fighter. Though he does not initially have superhuman abilities, his martial arts background allows him to engage in combat effectively. His connection to the Riderman legacy becomes literal when he adopts the mantle of Riderman, using equipment such as a Cassette Arm mounted on his left arm that can fire a steel cable to restrain enemies. This transformation is rooted in a childhood rivalry with his brother: as boys, Ichiyo would always play the role of Kamen Rider V3 while forcing Mitsuba to be the supporting Riderman. After a fight in which Ichiyo accidentally broke Mitsuba’s left arm, Ichiyo gave him a Riderman mask, telling him he would be the partner. Mitsuba initially resented the assignment, but over time he came to admire Riderman for being a human with a cybernetic arm rather than a full cyborg, embracing the role as his own.

His key relationships include his brother Ichiyo, who operates as a V3-inspired vigilante, and Yukarisu, a woman who becomes his romantic interest and is later revealed to be connected to Shocker. In a critical encounter, Yukarisu is placed under mental control by a kaijin, but Mitsuba frees her by declaring his love, demonstrating the depth of his commitment. His presence in the narrative serves as a bridge between the everyday world of the family restaurant and the extraordinary, often surreal ambitions of the other characters. By treating Tojima’s costumed identity with complete seriousness, Mitsuba validates the protagonist’s journey and reinforces the series’ theme that the spirit of heroism can be a tangible reality for those who believe in it. Through his eyes, the audience sees how childhood encounters and media influences can shape a person’s entire life mission.