Aoyagi Mitsuki
青柳 美月
Transforms into AkibaBlue on Hikounin Sentai AkibaRanger.
Played by Hinami Kyoko 日南響子
Name
Ao 青 is Blue. Yagi 柳 means Willow. Aoyagi 青柳 together means "Trough shell, short-necked clam". And Mitsuki 美月 means "Beautiful Moon".
In her rollcall with Takuma, I believe she mentions a deep sea treasure, which is essentially what a pearl is.
Character
Apparently a high school girl who is interested in martial arts. She's frequently seen doing exercises in the Hidden Base cafe. Unlike Red and Yellow, Mitsuki is not a Sentai otaku, but she apparently is a fan of anime Z-Cune Aoi.
As the series goes on, Mitsuki develops an admiration for the action in Sentai. Especially stunt actor Niibori Kazuo. Apparently imitating one of the stunts that she saw on a Sentai worried her mother.
AkibaBlue
Stunt actress: Ooshima Haruka
Her helmet has a ponytail, even though Mitsuki has short straight hair. There's a bear on her bottom under the dress, which is something she and Red fight about in the opening scene.
At first, Mitsuki is apathetic about the rollcall. After training with Niibori, she learns the importance of stating one's name. From that point on, she states her name rather elaborately, often involving a lot of movements, and a pause between "Akiba" and "Blue".
While her comrades were in a drunken stupor, underage Mitsuki was studying Boukenger episodes. In the same episode, she summons BoukenRed who is voiced by Takahashi Mitsuomi the actor for Akashi. Akashi tells her to try his Outrageous Power, the Bouken Scooper, which is DaiBouken's weapon.
Later on, Mitsuki trains with famous stunt actor Niibori Kazuo. One of his roles, the red Jetman, comes out of the sky to help the AkibaRangers at the end of the episode. This gives AkibaRed Jetman's wings.