Kaoru Shiba

"Shinken Red~Kaoru Shiba" "Super Shinken Red! Going Forth!"

Kaoru Shiba (志葉 薫, Shiba Kaoru) is the true 18th head of the Shiba House, a position that Takeru was holding in her place. She is referred to by her vassals and servants as Princess (姫, Hime).

Shinkenger
As the 17-year-old head of the Shiba House, Kaoru is the one who possesses the knowledge of sealing the Gedoushu. Due to this, she stayed in hiding while Takeru acted as her kagemusha to keep the Gedoushu away from her. However, refusing to hide, and perfecting the sealing character, Kaoru takes back her title and assumes her birthright.

Even though it could be hinted that her appearance would open up a ridge between Takeru and the other Shinkengers (especially seen as how Takeru's childhood friend Genta appeared to dislike her at first), they stood loyal neither to the Shinken Red figure, nor to the figure of the head of the Shiba house, but to Takeru as a person, which Kaoru understood and accepted, eventually adopting him to make him her legitimate successor as the head of the Shiba clan. (i.e. She became his adoptive mother even though she is younger than him)

Like Takeru, Kaoru has the ability to become Shinken Red and can use the Inromaru to transform into Super Shinken Red.

Although she was disliked by Genta at first for the reason that she had usurped Takeru as head of the Shiba Clan, she soon showed that she was very kind and caring, which won him and the other Shinkengers over. However, like Takeru, Kaoru tends to holds her emotions back. Oftentimes her retainer Toshizo Tanba annoys her, as he usually sticks to his arrogant views thus essentially acting as a foil to her. Whenever it happens, she responds by hitting him on the head with a fan to show her displeasure.

Kaoru attempted to seal Doukoku away with the sealing character she had spent her lifetime learning, however it failed due to his absorbing Dayuu. As a result, she was badly injured and resigned as the 18th head, adopting Takeru as her son and officially making him the 19th head of the Shiba Clan. At the end of the season she is seen saying goodbye to Takeru. Following this, Tanba suggested she get married but she then sternly says, "Too soon".

Gokaiger
Kaoru fought in the Great Legend War, along with the first 34 Super Sentai teams. She, along with everyone else, sacrificed their powers to destroy the Zangyack armada. Kaoru's Ranger Key, along with those of the 9 other Extra Heroes, ended up in the hands of Basco ta Jolokia.

When the Gokaigers appear searching for a samurai, she challenges them to retrieve the Shinkenger Ranger Keys, and Joe Gibken challenges her to allow the other Gokaigers to fight the Zangyack forces. When she realizes that the Gokaigers fight for good, she uses her kuroko to help them when Captain Marvelous is injured in battle.

The copy of Princess Shinken Red appeared when Basco united his nine remaining Extra Hero copies, his Black Knight key having been taking by Gai in his failed attempt to gain the Greater Power of Gingaman, when he was confronted by Gorou Hoshino (OhRed). The Extra Heroes would then fight the Gokaigers again, who wished to take the Ohranger's greater power rather than just be given it. Princess Shinken Red's copy fought Luka (GokaiYellow). The Extra Heroes were taken down by the Olé Bazooka. Princess Shinken Red's Key, along with the rest of the Extra Heroes was claimed by Gai.

After the Gokaigers defeated the Zangyack emperor, she got her powers back as did her team.

Shinken Red
As Shinken Red (シンケンレッド, Shinken Reddo), she is the Samurai of Fire (火の侍, Hi no Samurai) and can use the Inromaru by itself to become Super Shinken Red (スーパーシンケンレッド, Sūpā Shinken Reddo).

Ranger Key
The Princess Shinken Red Ranger Key (姫シンケンレッドレンジャーキー) is Kaoru Shiba's personal Ranger Key and what became of her powers after she along with the rest of the 34 Super Sentai sacrificed their powers to end the Great Legend War.

This key along with the other nine extra hero keys and the fifteen sixth ranger keys, were initally acquired by Basco ta Jolokia and later used by the Gokaigers. Like all of his Ranger Keys, Basco used his trumpet, the Rapparatta, to turn the Princess Shinken Red key into a puppet to do his bidding. Basco united his nine remaining Ranger Keys when he was confronted by Gorou Hoshino (OhRed†). The Extra Heroes would then fight the Gokaigers again, who wished to take the Ohrangers' greater power rather than just be given it. Princess Shinken Red fought Luka Millfy (Gokai Yellow), who fought as OhYellow. The Princess Shinken Red key, along with the rest of the Extra Heroes was claimed by the Gokaigers.

While in the possession of the Gokaigers, the Princess Shinken Red Ranger Key was used once by Ahim de Famille (Gokai Pink) and twice by Luka Millfy (Gokai Yellow).

After Zangyack were finally defeated, the Gokaigers gave the Ranger Keys back to their rightful owners. It is presumed that Kaoru received her key and became Princess Shinken Red.

Trivia

 * Despite popular belief, Kaoru is not canonically the first female Red Ranger in Super Sentai, nor the first female Shinken Red: both were her predecessor, Sakuya Shiba. However, she is the first female Red Ranger to actually make an appearance in a Super Sentai Series installment.
 * Kaoru is the first replacement leader of the entire Super Sentai franchise since Takayuki Hiba (VulEagle II) of Taiyou Sentai Sun Vulcan.
 * Unlike Takayuki, she didn't permanently replace Takeru. Neither of them lost their their powers when the other became the leader.
 * Coincidentally, both Kaoru and Takayuki appear as their teams' main representatives in Kaizoku Sentai Gokaiger.
 * Kaoru's character is 17-years-old in Shinkenger, but her actress, Runa Natsui, was 14 at the time.
 * The appearance of Kaoru in Gokaiger instead of Takeru is most likely because she was meant to be Shinken Red in the first place. It could also symbolize her being the first female Red Ranger in Super Sentai (although her appearance could be for the less symbolic reason that Takeru's actor, Tori Matsuzaka, wasn't available).
 * Princess Shinken Red has her own unique Ranger Key in Kaizoku Sentai Gokaiger despite the fact that, apart from her suit being a standard female member design, her powers in no way differ from Takeru's. This is because the powers are duplicated. Although they never fight side-by-side, both Shinken Reds are implied to be able to transform at the same time since they each have their own Shodophone, as Kaoru never took Takeru's from him. However, it should be noted that prior to the Legend War, there was not one scene where Takeru and Kaoru were shown to use the Shinken Red powers at the exact same time. Every time one was using the power, the other was in a situation where, coincidentally, the power was not used.
 * Ironically, the only time both Shinken Reds were seen fighting together, it wasn't Takeru or Kaoru: It was Captain Marvelous and Ahim de Famille, normally Gokai Red and Gokai Pink, in Something I Don't Want to Lose.