Miho Kirishima is a young woman who becomes a participant in the Rider War as Kamen Rider Femme, a role that marks her as the first official female Kamen Rider. Her background is rooted in tragedy: her older sister was murdered by Takeshi Asakura, a violent criminal who later becomes Kamen Rider Ouja. Driven by grief and a desperate hope, Miho accepts Shiro Kanzaki's proposal to join the Rider War for two intertwined reasons: she wants to use the winner's wish to resurrect her sister, and she seeks personal vengeance against Asakura. To fund the expensive cryogenic preservation of her sister's body while waiting for the resurrection, Miho operates as a con artist, using her charm and beauty to seduce wealthy men and steal their money or valuables. This morally ambiguous lifestyle reveals a pragmatic and somewhat cynical side to her personality; she is willing to use any means necessary to achieve her goals, remarking that she has to win no matter how dirty her methods become. Despite this hardened exterior, she is not entirely cold. Her interactions with Shinji Kido, Kamen Rider Ryuki, show a more vulnerable side. She initially tries to manipulate him, even attempting to steal his Advent Deck, but she grows drawn to his earnest and seemingly naive determination to stop the Rider War. Their relationship is marked by bickering and mutual suspicion, yet there are moments of genuine kindness and a bond that hints at a deeper, if conflicted, connection.

In the story, Miho's role is that of a vengeful and determined fighter who is outmatched in raw power by Asakura but refuses to back down. Her combat style as Kamen Rider Femme is agile and suited for engaging multiple opponents, in contrast to the more chivalrous one-on-one style of Kamen Rider Knight. She wields a rapier-like Blanc Visor and can summon a double-bladed naginata called the Wing Slasher, as well as the Wing Shield for defense. Her contract monster is Blancwing, a giant swan whose name combines the French word for white with the word wing. Blancwing serves as her mount and ally in battle. Her ultimate technique, the Misty Slash, involves Blancwing creating a powerful gust of wind that propels her enemies toward her waiting blade. Miho's development is marked by a growing awareness of the cost of the Rider War. She pushes herself into dangerous confrontations, and her obsession with defeating Asakura leads her to take reckless actions. After being saved from Ouja by Kamen Rider Ryuga, she mistakenly believes Ryuga is Shinji and invites him on a date, during which the evil duplicate attacks her. The injuries she sustains in the subsequent battle are fatal. Though Shinji arrives to help, she hides the severity of her wounds, shares a brief, smiling farewell with him, and then collapses. In her final moments, she apologizes to her sister for not being able to bring her back, and dies. In the Kamen Rider Ryuki Special: 13 Riders, Miho appears solely as Kamen Rider Femme during the final battle, fighting alongside the other remaining Riders against Shinji and Ren. Her character in the special is consistent with her portrayal in the movie, serving as one of the thirteen combatants in the war, though her personal backstory and motivations are not explored within the special itself.