Mitsuru Sano is the human identity of Kamen Rider Impaler, one of the thirteen participants in the Rider Fight. He comes from a wealthy family; his father, the president of a major industrial company, disowned him two years before the events of the story, sending him out into the world to learn the hardships of life. During this period, Mitsuru works in a parking garage, occasionally cleaning rich people's cars, and lives in a modest apartment. After his father dies and leaves behind a massive inheritance, Mitsuru suddenly becomes rich and powerful, inheriting his father’s company.

Mitsuru’s personality is defined by a deep naivety and a misplaced belief that money can buy everything, including friendship, respect, and love. He is eager to please and desperate to belong, often approaching other Riders with a puppy-like enthusiasm, handing out business cards that identify him as Kamen Rider Impaler. He refers to more experienced Riders like Shinji Kido and Ren Akiyama as his seniors, hoping to be accepted into their group. When rejected, he pouts and moves on to the next potential ally, showing a lack of understanding of genuine human connection. His motivations for becoming a Rider are initially rooted in a desire to attain wealth and a happy life, but once he inherits his father’s fortune, he tries to withdraw from the Rider Fight. He learns that if he abandons his contract with his Mirror Monsters—the Gigazelle herd—they will kill him, so he is forced to continue.

In the story, Mitsuru attempts to use his inheritance to buy the allegiance of other Riders, carrying a suitcase full of cash. He first approaches Shinji and Ren, who reject the offer; Shinji angrily tells him that loyalty cannot be bought, while Ren shows a momentary interest but ultimately lets the money go. He then approaches Shuichi Kitaoka, who feigns agreement and plans to take advantage of him, but Mitsuru later cancels the arrangement after deeming Kitaoka unreliable. He eventually turns to Tiger, Shuichi Toujou, believing he is the only one he can trust. This trust is misplaced; Tiger betrays and severely wounds him. Despite being saved by Ryuki, Mitsuru stumbles into the path of Ouja, who destroys his card deck, leaving him trapped in the Mirror World. There he sees a vision of a young woman waiting for him in the rain—a girl he had recently met and begun to form a sincere relationship with—and dies clutching a shard of mirror, anguished by the life he could have had.

Key relationships include his failed attempts to ally with Shinji Kido and Ren Akiyama, his manipulation by Kitaoka, and his betrayal by Toujou. He also briefly tries to align with Asakura, the violent Ouja, out of ignorance of the man’s true nature. His most positive connection is the daughter of a business associate, who sincerely returns his interest, but this potential happiness is cut short by his death. His development traces a tragic arc from a naive, money-driven young man to a desperate victim of the Rider Fight, ultimately realizing too late that his approach to life was wrong.

As Kamen Rider Impaler, Mitsuru is a melee-based fighter whose style incorporates Muay Thai techniques, particularly powerful knee strikes delivered through his Gazelle Visor. He wields a Spin Vent that equips his right arm with a large double-drill gauntlet for stabbing attacks. His unique ability is commanding a herd of gazelle-type Mirror Monsters—Gigazelle, Megazelle, and Omegazelle—which travel and attack as a pack, often overwhelming opponents through numbers. His Final Vent, Drive Divider, summons the entire herd to strike the enemy in unison before he delivers a devastating knee to the head. Despite this combat power, Mitsuru has no formal fighting experience and relies heavily on his monsters, which sometimes become unruly and attack him if not controlled.