Ai

Ai is Sai's (X) partner in crime. She handles most of the cleaning up at the crime scenes. She is also the one who enforces Sai's Phantom Thief X image and status by prompting him to take something from each place he murders in. X finds this rather troublesome, though, and usually grabs the closest thing available to pass to Ai. Because of this, Ai had stated that her house has been piling up with B-grade goods. Before she met Sai, Ai was previously a plane bomber who went by the name of Plane Crasher Imina. She was notorious for bombing planes during flights but the authorities could not catch her due to her elusiveness. During her time as Imina, she worked for a bigger group of people and continued her job feeling the limitations of humans, wanting to go on through life without worrying about those limits. She encounters X for the first time on a flight to San Fransisco, and while surprised, she quickly grew attracted to his nature. After getting off the plane, she learns her higher-ups had planned to doublecross her to use her as a gift for the government of the country so that they could start off on a clean slate again. She leaves X to deal with the men, and joins X's side after that. Depending on the day, she refers Sai as Master, child, friend, lover, brother, sister or others. Source: Wikipedia, Neuro Wiki