Chiyoko was a seemingly human girl of Japanese descent.
Biography
Chiyoko was first seen in an alliance with Axos, who had come to 21st century Tokyo to set up a fake company, which they called the Rising Sun Corporation. One of the corporation's "products" was a drink called "Goruda". Goruda was advertised as a brain tonic, but it would actually transform those who consumed it repeatedly into Axons. In its public face of "Mr. Kin", Axos passed off Chiyoko as 'his' ward and advisor.
When Axos encountered resistance from the Eleventh Doctor and his allies, Chiyoko betrayed it, freeing the Doctor's companion, Amy Pond, and Major Harada of UNIT. When the Doctor defeated Axos, the dying gestalt claimed that Chiyoko had promised it Earth. Chiyoko replied by saying the deception was necessary "for a new life to begin." (DWM: The Golden Ones)
Chiyoko then somehow managed to travel to Paris, France, 1858, where she watched the Doctor and Amy depart. (DWM: The Screams of Death)
It was revealed that Chiyoko was an evolved amalgamation of the Doctor's TARDIS, Axos, the Shasarak, Konami, Cosette and Margaret Webster. She had what looked like a galaxy on her chest, and she destroyed a whole army of plague robots. She had the ability to see through time, and could travel through time, due to her TARDIS-like qualities. (DWM: Apotheosis)
After leaving the Doctor and Amy, Chiyoko travelled through time, freeing Axos from the time loop, sending Valdemar to 19th century France, and transporting the Vorlax Regeneration Drone to 2011, thus setting in motion the events that would lead to her own creation. She then travelled thousands of years iunto Earth's future and instigated a war between the humans and the Galateans, with herself worshipped as a god by both sides. When the Doctor and Amy failed to stop a bomb from destroying the Earth, Chiyoko appeared to them, telling them that the purpose of the war was to see which race would be the victor. She decided that the Galateans would be allowed to continue while the humans would have to 'go away'. She then left Earth moments before it was destroyed.
She later founded the Museum of Lost Opportunities, a museum tributing the Earth and the human race, and to remind herself why the Humans deserved to die.
She was present at the activation of the first Galateans. She put the Doctor, Amy and Alan Turing out of sync with normal time to stop them from interfering. When Keltor Jacobs tried to shut the Galateans down she killed him. She then took the Doctor, Amy and Alan to the Planet Kepler IV 1,000 years later to show them the extent of the war between the Humans and the Galateans. Afterwards, she took them back to Earth on the day of its destruction, in the hope that they would perish. However, she was unsuccessfull, as they managed to get themselves Time Scooped back to the Museum of Lost Opportunities. She followed them there and deactivated the Brontë sisters. However, before she could kill the Doctor and Amy, the Doctor used the Time Scoop to bring Cosette, Konami and Margaret (from points in there timestreams before they were absorbed by the TARDIS) to the Museum. This endangered Chiyoko's existence and greatly limited her powers. The Doctor tried to convince Chiyoko to undo her existence and let the lifeforms she was made of live. Chiyoko, who was now feeling great regret, pain and sadness, did so. Before she died, the Doctor took her back in time, and with the help of Alan Turing, he was successful in preventing the Galatean rebellion. He then upload Chiyoko's mind into a Galatean body, allowing her to continue her life safely. (DWM: The Child of Time)