Like many Asari, Rili was born on Thessia, the Asari home planet. Despite never knowing of her father, she's been told on countless occasions by her mother that he was a respectable individual that she loved dearly. Naive and small, Rili never paid much attention to her mother's vagueness, instead interested in the world around her. Thessia was beautiful, and to a young Asari, the perfect playground at a young age. A playground that, as Rili got older, she would outgrow and desire for something more.
This longing for change became apparent once the first signs that she, like many Asari, had a natural semblance for biotics. As soon as Rili was recognized that she had an adept ability for the control of biotics, there wasn't anything else that she'd want to do than join the military and further develop this gift. A gift that her mother felt was more of a nuisance than useful. Rili's mother felt that developing her biotics would ultimately prove fruitless, as there hadn't been any sign of war for the Asari in her lifespan, and as such she felt there wouldn't be a need for her daughter to train on the off chance there was one. But Rili was persistent, and when she was able to, signed up to begin training as an Asari huntress at the age of 50.
For the next 30 years, Rili devoted her life to studying various aspects of martial arts, sharpening her mind and body, and perfecting her biotic abilities. Biotics were an essential part in her training, as she knew that, if she lacked biotic talent, there was a high possibility that she would be forced to leave military service... And she didn't mind that. In fact, it inspired her to grow, to become stronger for the sake of her people. She believed that, despite a relative peaceful galaxy, there would always be some sort of evil to deal with. But the higher ups had other wants for her. Despite showing extensive prowess for combat, they felt as if there was enough of those as is. And so, they set her aside, instead having her do the all important...
Study of other races. Infuriated, but compliant, the Asari above her believed that, if she were to be truly effective, she would need to do extensive research on the other species within the galaxy, which at the time, was 13 years before the relay 314 incident of the Turians, and thus giving her that much time to herself. If she would be honest with herself, she felt cheated, but instead of dwelling on her discontent, Rili took it upon herself to read as much and study the other species of the galaxy. These studies ranged from simple history to biology, and everything in between. Preferred weapons, biotic abilities, medi-gel effeciency/recipes... Rili made sure that she could find out all that she could about them. She essentially had all the time in the world to devote to this cause, and while it wasn't the excitement that she desired, it gave her much needed insight for when she would eventually leave Thessia. Not to mention that, whenever she would get bored, she made sure to not falter in practicing and maintaining her combat skills.
Fast forward to after the first contact war of humans, and Rili is given a new galactic species to observe and study: the humans. She took note of how, despite their relative short lifespan, they were aggressive in their desires, striding forward with confidence in themselves despite not really knowing what they were getting into. To Rili, they were inspiring, but scary. They could accomplish things that she thought would take centuries to even train in, all due to their dedication to become something more...
To her, Commander Shepard was a prime example of such a person. Skilled, tactical... easy on the eyes. She admired him as the first human Spectre, and seeing him become one inspired her to increase her time dedicated to training herself aside from her studies. Often, she found herself visiting the Citadel during her off periods, giving herself a type of shore leave up until Seren's attack on the Citadel.
The shock of the initial contact with a reaper made her superiors begin to quietly bring back those they had set aside, and gladly throughout the events of Shepard's battle against the collectors, Rili was back on Thessia, doing what she loved: Practicing her biotics. She was training to become a Commando during the two year gap between Shepard's supposed death and his eventual victory against the collectors, she was so close to a promotion.
But nothing could prepare her for the end of the world. Despite her relatively young age for an Asari Huntress, hastily she was promoted due to the chaos that occurred thanks to the reaper attack on Thessia. The Asari had grown overconfident in themselves, and Rili was on the front lines, doing what she could to protect everything she cared about. But nothing could prepare her for that sudden responsibility to have been tossed at her. When the reapers touched down, Rili was filled with confidence, but that confidence would devolve as the situation became ever grim. To think, this was what she wanted... And yet upon it actually happening, upon something interesting occurring in her life, and it was immensely worse than she or the galaxy had anticipated. Slowly and surely, they were being pushed back despite their best efforts. Her powerful biotics unleashed could only do so much against a seemingly endless wave of monstrosities, and it seemed that as she decimated the enemy, a horde would take their place. But Shepard had recently been to Thessia when the reaper's first appeared, and surely, she thought, he'd have an answer to this. All they'd have to do was survive for a little while longer.
By the time Shepard had set off the Crucible, Rili's squad was surrounded by Husks, pounding at the barrier that she had created around herself with the last remaining strength she had. She could hear their screeches, their desire to tear apart added onto her fear of death and sorrow. But miraculously, as she stared towards the sky, she noticed an intense light spreading across the horizon and hastily erasing the creature around her, and allowing her to survive another day, and by extension the massive amount of refugees and civilians of Thessias she was meant to protect.
It was over, and yet... Rili felt a burning hatred for her superiors. They had spent countless years wasting potential to build up their army, like every other galactic race, and it infuriated her immensely. So many died due to their carelessness, and despite her best efforts, everyone she knew was most likely dead because she wasn't strong enough to protect them. While she was hailed as a hero during reconstruction for defending Thessia and for her excellence in biotics, at her first opportunity she left her homeworld and didn't want to look back. Instead, she thought it would be best to put her knowledge of other species biology to good use, and knowing that there were so many wounded, ultimately decided to be a wandering doctor for those who needed it.