More than just a defense attorney, Calisto Yew joined prosecutor Byrne Faraday and detective Tyrell Badd to become the Great Thief Yatagarasu after a case which couldn't be solved by traditional means. Although she pretended to be the hurt sister of a victim, her identity was a ruse and she was a plant in order to monitor Faraday and Badd's actions by the smuggling group that they were trying to track down. Eventually, she killed Faraday, but she was caught by a young Miles Edgeworth. She managed to elude capture and continued to act as a spy for the smuggling organization when she joined Interpol under the name of Shih-na, acting as the assistant to Shi-Long Lang, who was one of the key investigators on the case. She wound up being discovered by Edgeworth a second time, seven years after their initial encounter, and she was taken to prison.
Life as the Yatagarasu
The Yatagarasu is a main character throughout Miles Edgeworth: Ace Attorney Investigations, and serves as one of the main themes that ties all of the cases together. While not physically present for most of the game the character is discussed at length by the characters and silhouetted in flashbacks. Little is known about the great thief for the majority of the game, other than Kay Faraday's assertion that her father (Byrne Faraday) was the Yatagarasu. The police and certain individuals have been chasing the Yatagarasu for years with no success and are unable to learn anything about the thief's identity.
The Yatagarasu steals objects from specific people who the thief believes are guilty of a crime, and then sends the stolen item to the media along with a calling card to prove who stole it. A calling card is never sent to announce a crime, unlike the thief from Phoenix Wright: Ace Attorney - Trials and Tribulations, 'MaskDemaske'. The item in question is always evidence related to a crime committed by the victim of the theft, and is sent to the media to provoke action or expose the crime that the police were unaware of. Tyrell Badd, the detective in charge of pursuing the Yatagarasu has been profiling the thief for many years and is considered an expert on the thief's MO.
In the final case 'Turnabout Ablaze' it is revealed that the great thief Yatagarasu is not a single person, rather a team of 3 people comprised of Calisto Yew (defence lawyer, Byrne Faraday (prosecution lawyer) and Tyrell Badd (detective). It is revealed that they formed the group to expose and bring to justice criminals who they felt needed to be brought to justice outside the restrictions of the law. Each of the members brought a unique ability to the group which built the Yatagarasu's reputation. Yew, as a defence lawyer, was able to learn secrets about people suspected of committing crimes. Faraday invented the device Little Thief that was able to bypass any security system and allowed them to enter the target area undetected. Badd, as a detective, was able to pretend to investigate the crime while covering up and destroying any incriminating evidence.
The Fake Yatagarasu
The real Yatagarasu's activities ended in the KG-8 incident, where Byrne Faraday was murdered by Calisto Yew. Taking full responsibility for the Yatagarasu herself after being exposed by Miles Edgeworth, Yew fled and was not seen for many years. In the present time a calling card claiming to be from the Yatagarasu is sent to Miles Edgeworth. Since the breakup of the real Yatagarasu was not known it is assumed that this is the same Yatagarasu, until the final case where everything is revealed.
Kay Faraday, Miles Edgeworth's sidekick/assistant in the game is introduced claiming she is the heiress to the Yatagarasu name inheriting the title from her father, Byrne Faraday who she believes to have been the original Yatagarasu after finding diary entries and the Yatagarasu's signature tool: Little Thief. Kay makes her first appearance in Case 3: The Kidnapped Turnabout where she reveals that she is the great thief much to Edgeworth's surprise, and is confused as to how she became the second Yatagarasu which is explored throughout the rest of the game.
The Future of the Yatagarasu
In the epilogue of Miles Edgeworth: Ace Attorney Investigations Kay suggests that a new Yatagarasu team should be formed, reacting to the revelation that her father did not act alone as the Yatagarasu but as a team of 3. She coerces Miles Edgeworth and Detective Gumshoe to form the group as they are her friends and they also share similar qualities and job positions to that of the original Yatagarasu. This is partly to redeem the name of her father's secret identity in reaction to the crimes committed by the fake Yatagarasu, but also to continue his work to expose criminals.
The Yatagarasu is named after the mythological creature of the same name originating from Asia, known as a bird with 3 legs (in this case a raven). The character is named Yatagarasu due to the logo/illustration featured on the costume of the second Yatagarasu (worn by Kay Faraday) as well as appearing on the calling card the great thief sends with the stolen item to the media. Each of the legs represents a member of the group. The Yatagarasu name has been used in other games and TV shows such as a persona in Persona 4 but they are unrelated as characters.