Depressed by the fact that she and Shepard could not have a proper family (as Quarians and humans cannot interbreed), but still desiring a child of her own, Tali turned to genetic engineering in hopes of finding a solution. However, the mainstream information was fruitless, so Tali decided to go after more restricted information. In the process of hacking the database of a major company, Tali detected a bizarre anomaly unlike any other she had ever seen. Curious, she attempted to pinpoint it, which resulted in her inadvertantly creating a digital field, which allowed Renamon to step out of the Digital World. Fascinated and inspired by the process of creating false proteins that allowed digimon to enter the world, Tali pleaded with Renamon to allow her to use Renamon as a basis to finally obtain her much-desired child. Renamon was, thankfully, agreeable.
What followed was months of study and experimentation. Finally, Tali, having worked tirelessly and in secret, managed to create the false proteins. Now with the ability to create a body for her pseudo-offspring, she set about making its mind. To this end, she crafted an elaborate AI in a flawless mimicry of the human (for lack of a better word) mind. The AI was capable of changing, and was capable of altering due to external stimulus and experience. This was to allow Tali's construct the appearance of mental growth. She also took a randomized list of mental traits of Shepard and herself and added them into the AI's personality core. In honour and recognition of Renamon's assistance in her mission, Tali named the AI "Rey", a fragment of an old Earth word meaning "fox".
On the night of Rey's "conception", however, things went somewhat awry. Tali accidentally selected a somewhat altered design of Renamon (smaller, and blue), which she had originally intended to use to create a companion for her pseudo-child, instead of the original blue-print, when she finally created the child. In dismay, Tali begged the Digimon to take the child, but before Renamon could say yes or no, she was sucked back into the Digital world, leaving Tali with her child-like Mistake.
Rey's personality is mainly made up of a list of mental traits from Shepard and Tali's psychological profiles. However, the AI can change just as a real person might. What really stands out, though, is that Rey has "inherited" Shepard's strong moral center, Tali's tendency to babble when nervous, an extreme survival instinct from Shepard, and a strong sense of loyalty from both. According to other information on her, she is exceedingly optimistic, as well as a little on the idealistic side.
Abilities and skills
Being inherently connected to the Digital world (though Rey doesn't know it), Rey is an intuitive hacker, decrypter, and has an instinctive understanding of computers, cybernetics, and similar technologies. This makes Rey a natural Engineer. It has yet to be seen if Rey has any powers or abilites like a Digimon.