There is little to be said about the childhood of Kali'Zael nar Stalingrad that cannot be said about that of the majority of quarians. The only slight difference lies in the role of the Stalingrad, a newer addition to the Migrant Fleet bought cheaply from the Systems Alliance, as one of the smallest branch of the Fleet: Special Projects. The child of two scientific researchers working to advance quarian technology for the good of the Fleet, Kali developed an interest in and passion for technology and science beyond even the typical quarian affinity. Her childhood aboard a Special Projects ship rather than one of the Civilian Fleet had little effect on Kali's appropriation of quarian values, however - life aboard the Flotilla is hard, regardless of which segment one's ship belongs to, and the community-oriented mindset and values of loyalty and trust hold strong in Kali.
Her inheritance of her parents' fiercely inquisitive and independent scientific minds, however, would prove to be difficult for Kali. An inquisitive mind cannot help but to pursue knowledge of the forbidden - just as Eve caved to the temptation of the apple, so did Kali seek knowledge on that most taboo of subjects: AI. Her passion for technology and progress led her down the very same faulty path that led her people to exile, and that, shortly prior to her emergence into this story, would see Kali caught in the battle for Rannoch.
This interest in, and lack of aversion to, artificial intelligence was but a small variation in Kali's life compared to many quarians. It is, ironically, the smallest of changes that can produce the largest of end differences, however. Many quarians leave for their Pilgrimage with little idea of what they wish to return with; the spirit is one of adventure, of opening oneself to life beyond the Fleet and so gaining an appreciation of what one has, of learning and discovery. Kali, by contrast, knew exactly what she wished to return with: research on that which she should fear and avoid, but instead was only curious of. Under the pretense of seeking to research how diseases proliferate and develop in overpopulated environments - an eternal fear for the immunologically-impaired quarians living aboard the cramped Fleet - Kali departed for Omega: a place that worked with her cover story due to its overpopulation and lack of a central government to regulate the frequent rampant illnesses; and a place lawless enough that she could study what she wished without fear of the Council's limitations on AI research.
It is important to note that Kali did not do this lightly, or out of a desire simply to rebel or cause destruction. To Kali, science is but a tool, a key that can unlock any door, inherently devoid of morality - and so only ever destructive or evil in how we, as people, use it. To her, progress is always the ultimate goal, and to stifle progress and knowledge because of potential risks is tantamount to a cardinal sin. In other words, she believes fully that her research can be used to benefit the quarians in some way, as long as it is applied correctly - either in eradicating an archaic and outdated fear of virtual and artificial intelligences that is only restricting the quarians from their potential, or in revealing weaknesses in them that can be used to eventually retake their homeworld from the geth. Her own curiosity is what drove her, but she could justify her actions with this reasoning; she could believe that she was not only satisfying her own curiosity, but also the needs of the Fleet.
And so it was that Kali arrived on Omega: young, arguably naive, and alone. Culture shock is normal for quarians leaving the Fleet for the first time, but most do not immediately travel from the most selfless of places to the most selfish. It suffices to say that it was not long until she learned to defend herself, learning to become a much harder and less trusting person than she had been on the Fleet. Nowadays her small, cosy apartment, lined with colourful quilts as a reminder of home, is secured with an electronic lock that only the most talented of hackers could crack - one she designed herself.
A lock. Privacy. A notion that was inconceivable back on the Flotilla. Although her research progress was slow, it was not long until Kali fell in love with the free way of life the rough inhabitants of Omega possessed. It would be a lie to say she did not miss home, but her heart and mind were opened to other ways of life. Her curious mind had secretly always longed to know what it was like to experience something different - to experience something extraordinary, special - and now that desire was realised. Perhaps it was this that drove her towards the subject she chose to study, too. She would never think of Omega as home, abhoring the blatant criminality of the place and the selfishness of its inhabitants, but she came to love the freedom that accompanied an independent life.
And there is nothing more precious to a quarian than home. In a galaxy where the quarians belong nowhere and are constantly looked down upon, the concept of belonging is fundamentally valued beyond almost all else.
The appearance of the Reapers, that which threatened the very existence of the galaxy, caused a monumental perspective shift for everybody in the galaxy – Kali amongst them. Suddenly, her home, that which was so vital to her, was to be under threat of attack and destruction. Pilgrimages and research seemed suddenly comparatively unimportant, even though she knew her research could potentially be useful for combating the Reapers, synthetics as they are. It was a difficult decision, but in the end the typically quarian sense of community won out over her more self-interested desires to continue with the life of individual freedom she had found. Kali returned to the Migrant Fleet urgently; and once there, enlisted with the Migrant Fleet Marines. She could not continue her research once home, and to this day her activities during that time remain a closely-guarded secret, and so she decided the best way to serve was a more proactive one – a need for proactiveness as opposed to passiveness in her efforts perhaps stemming from the shift in life perspective generated by her time on Omega.
And so it came that Kali was in the thick of the fighting on Rannoch. Not being a battle-hardened soldier, the horror and violence played out across the sacred earth of her homeworld – that which her people had longed to recapture for centuries – scarred her. Never had she been a violent person, and although Omega had left her significantly less naïve than she had been prior to her Pilgrimage, it was no preparation for the type of all-out and brutal war the Reapers brought to the doorstep of every home in the galaxy. Despite this, she could not help but to rejoice at the reclamation of her homeland, completely oblivious to the actions of Shepard and Tali'Zorah that had led to it until after they had already departed. The joy of that moment is, perhaps, the only reason she could continue to fight beyond that dreadful battle.
The Migrant Fleet, now officially part of the galactic war effort, was obliged to contribute soldiers to the cause. Kali had distinguished herself in battle, and so was selected for this purpose – indeed, to head into particularly dangerous combat situations. Kali was deployed to Nevos.
The fact that her success was attributed to her combat ability and not her (secret) extensive knowledge of AI synthetics almost certainly led to an over-inflated view of her by her commanding officers was, of course, kept close to Kali's chest. At heart she was still a scientist, not a soldier. She fought down her concerns, and would come to regret it.