Push

Like other governments, in 1945 the United States has set up a "Division" to secretly experiment on people with psychic abilities, hoping to build a powerful psychic army. Two "Movers", Nick Gant and his father Jonah, are running from Agent Carver, a Division "Pusher". Jonah tells Nick of a vision he received from a "Watcher" about a young girl he must help in the future in order to take down Division. Jonah helps Nick escape just before Carver kills Jonah.
Ten years later, Nick is hiding in Hong Kong. Carver tests a powers boosting drug, which has killed all previous subjects, on a Pusher named Kira. The drug works, a major breakthrough for the US program, but Kira steals a syringe of the augmentation drug and escapes. Carver can not let the drug fall into the hands of other governments. Cassie Holmes, a 13-year-old Watcher, arrives at Nick's apartment, explaining that they are going to find a mysterious case that will help them take down Division. The case is also sought by the Pop Family, a large Triad led by "Bleeder" Pop Father and joined by his two Bleeder sons and his Watcher daughter, Pop Girl.
Nick and Cassie follow her predictions to a nightclub, finding Nick's friend Hook, a "Shifter". He tells them to go to a "Sniff" named Emily, one of many Sniffs Carver and his right hand Mover, Victor, are trying to enlist to find Kira. With Emily's help, Nick finds Kira, revealed to be Nick's ex-girlfriend. Kira hid the syringe inside the case, then had a "Wiper" erase her memories to keep the Division Watchers off her trail. Nick recruits a "Shadow" named Pinky to "shade" Kira from psychic detection. Cassie finds a key in Kira's shoe to a locker high in a skyscraper construction site that is shaded by a powerful Shadow that Kira hired before her wipe.
To obstruct the Pop Family and Division Watchers, Nick gives his allies instructions in envelopes to open at specific times, then has a Wiper erase his memories. Meanwhile, Hook retrieves the case from the construction site and creates a duplicate, carrying a duplicate syringe. As part of the plan, Kira surrenders herself to Carver, who pushes her to believe that she is actually a Division agent who volunteered to take the augmentation injection.
Pop Girl corners Cassie at a secluded spot but The Wiper appears at the right moment to incapacitate Pop Girl with a massive memory wipe. Nick meets with Carver, Victor and Kira to trade the drug for Kira's freedom but "Division Agent" Kira tells him their relationship, including a visit to Coney Island, was a false memory she pushed into his mind just yesterday. The three force Nick to take them to retrieve the case, where the Pop Family Triad soon ambushes them, wanting to sell the drug to another government for $6 million. Victor kills several assailants before Pop Father unleashes a powerful scream that kills Victor, upon which Nick kills Pop Father by pushing construction material on him.
Nick surprises Carver and grabs the syringe from him. Unable to convince Kira that their relationship was real, Nick jams the syringe into his arm, killing himself. After Carver and Kira leave, Nick wakes up. Cassie appears and retrieves the true case with the drug-filled syringe, revealing that Carver had found Hook's duplicated case, with Nick harmlessly injecting himself with soy sauce. The two now understand that Cassie's mother is so powerful a Watcher that she set the preceding events in motion before her capture by Division, even before Cassie's birth. By ensuring Cassie and Nick's eventual success, they can exchange the syringe with Division for Cassie's mother's release.
Flying back to America with Carver, Kira opens her purse and finds the envelope from Nick. Inside is photograph of Nick and herself together at Coney Island with a message: "KILL HIM. SEE U SOON. NICK" Kira pushes Carver to put his gun in his mouth and fire; the screen fades to black and a single gunshot is heard.

Question: Who is Nick's ex-girlfriend?
Answer: Kira