Jack

"Turns out, mess with someone's head enough, you can turn a scared little kid into an all powerful bitch. Fucking idiots."

Jack, also known as Subject Zero, is a human biotic who appears in Mass Effect 2. She is a potential romance interest for a male Shepard where it ends in two ways; a paragon ending for the relationship or a renegade ending.

Jack is voiced by Courtenay Taylor.

Subject Zero

 * Rank 1
 * Health: +5.00%
 * Weapon Damage: +6.00%
 * Power Recharge Time: -6.00%


 * Rank 2
 * Health: +10.00%
 * Weapon Damage: +12.00%
 * Power Recharge Time: -12.00%


 * Rank 3
 * Health: +15.00%
 * Weapon Damage: +18.00%
 * Power Recharge Time: -18.00%


 * Rank 4 Unlocks choice between Primal Adept or Primal Vanguard
 * Primal Adept: Jack can push her biotic abilities to the limit, greatly reducing recharge times of her powers.
 * Health: +20.00%
 * Weapon Damage: +18.00%
 * Power Recharge Time: -25.00%
 * Primal Vanguard: Jack focuses her ruthless energy into combat, heightening her weapon damage.
 * Health: +20.00%
 * Weapon Damage: +25.00%
 * Power Recharge Time: -18.00%

Dossier
A young woman with a mysterious and violent past, Jack was once the prime subject of a sizable Cerberus experiment to enhance biotic potential in humans. Referred to as Subject Zero she was the core of the project due to the success of integrating biotic enhancement into her. Many other children were also kept as part of the experiment and many died in trial runs of treatments to ensure that they would be successful on Zero. Kept separate from other children she grew up believing that the entire world was what she could see outside her window and repeatedly screamed herself voiceless while trying to communicate with others through her soundproofed cell. Eventually her powers grew to such a level that she became a serious threat to the staff, easily killing one by blasting him into a wall. These powers eventually allowed her to escape though details are presently unknown. After this the facility was shut down.

Having escaped Subject Zero went on to live a violent and bloody life. In order to sever ties with her past she took on the name Jack, and reacts violently whenever addressed by her former designation. She has killed various gangs, run with others, was a pirate for a while, crashed a space station into one of Kahje's moons, and at one point was a cult member, keeping her head shaved after her departure. Eventually she was captured and imprisoned in cryostasis on the Blue Suns operated prison ship Purgatory.

The tortures of her experimentation combined with her violent criminal lifestyle have rendered Jack a borderline psychopath, with a unpredictably violent nature and a fiery temper. She has an innate lust for combat, claiming to experience "warm feeling during a fight", along with a tendency to spout profanities constantly in conversation. Her body is covered head to toe in elaborate tattoos and scars, some are remnants of her experimentation while others mark kills and major events in her life. Having been used so many times by people in her life, Jack refuses to trust anyone and is clearly angered and confused by Shepard's attempts at conversation.

Yet underneath all this she is still tormented by memories of her past and longs for some kind of closure. She joins Shepard's team in exchange for Cerberus files detailing her experimentation after which she asks the commander to help her destroy the now abandoned facility.

Romance
Shortly after completing the mission at Horizon, during a conversation Shepard has the option to have casual sex with Jack. If Shepard agrees, a rough sex scene in the small quarters on the engineering deck occurs. However, after the sex scene, Jack refuses to speak to Shepard anymore, telling him to "fuck off" any time a conversation is attempted.

Should Shepard choose to turn down the casual sex option, get to know her first, and pursue a paragon relationship, the result is very different. Jack will eventually soften up and reveal a lot about her past, where on multiple occasions she was taken advantage of when she let her guard down. She also references a time where one partner chose to stay behind rather than abandon her to die, getting himself killed in the process. He left a recording on their shuttle for her in case he died, it talked about the future they were supposed to have, how he planned to set up with a home for them, about how he loved her and was sorry it wasn't going to happen. This implies a great deal of "survivors guilt" in Jack, from the incident and with her escape from Pragia. She eventually tells Shepard that she needs time to think about everything; it's all very new to her and she isn't quite sure what to do. En route to the final mission, she comes to Shepard in his cabin, tells him she has been thinking a lot about him, and that he's right and she needs someone. Jack gives in, and shows a very vulnerable and emotional side. Tears roll down her face as a tender scene ensues, culminating with her smiling peacefully as they lie together on his bed.

Suicide Mission
Jack is an excellent choice for projecting the biotic barrier for protection against the seeker swarms (provided she is loyal). If she is not loyal and trying to defend your squad from the seeker swarms, one of your squad members will die. To ensure a better chance of keeping her alive, purchase the subject zero biotic boost from the research station.

Trivia

 * If you bring Grunt with you to Purgatory to collect Jack, he'll have a particular interest in her after she is released and begins to escape. Grunt says such quotes as "Jack is small, this will be funny" and "Oh, I want to see this!" and "Move! I want to see how long she'll last" and "She's blowing everything up. I like her!" when pursuing her.
 * She periodically yells "I will destroy you!" and "I'll kill you!" when in combat and/or using abilities, akin to most humanoid enemies in Mass Effect.
 * Shortly after recruiting your first companion after Horizon, you will get the offer to sleep with Jack. Doing so however will not earn you the Paramour achievement.
 * Jack has, with the use of her biotic powers alone, destroyed both a military installation and an “ark ship” turned prison ship holding over four thousand prisoners. These were Pragia and Purgatory respectively.
 * Jack has a large Greek omega symbol on her back. This may refer to time spent on the outlaw Omega station but this is never confirmed.
 * Jack's extensive tattoos suited her personality better than clothing or armor. The final designs were intricately crafted as a visual story of her past.
 * According to Jack, she was once a member of a cult that betrayed her and used her for their own agenda. She also hints that she killed them all brutally for doing so. During this same conversation, she says that she shaved her head for the cult and has kept the haircut ever since.
 * Jack's name and shaved head might be a reference to the character Jack/Kyra from the Chronicles of Riddick movie series, more specifically the first movie Pitch Black.