Moriana was an earthbender who was from a medium sized village called Seloksu. Moriana would eventually become a member of the United Way movement and a good friend of the Vindicated Avenger.

Background
She grew up as a peasant who worked with her family in harmony until the Fire Nation raided the fields of her town and burned down multiple pastural homes. At the time Moriana was only seven and her nonbender father was slain when he tried to fight several Fire Nation troopers who were killing his livestock. Moriana was devastated but a team of Earth Kingdom soldiers eventually ran the Fire Nation troopers off after dispatching several of them.
Moriana's mother, Kutina, pushed her daughter to focus on school so she could find a profession that could take her out of the dangerous frontier. Moriana followed her mother's instructions to keep her happy but was secretly training to fight in her spare time. The girl made money beating up several boys in bets until her mother discovered the encounter and discouraged her. Moriana was promptly grounded and ordered to focus on her academics. A few other incidents like that would emerge until Moriana was 13 and earned a scholarship to attend a prestigious high school in the bustling city Yegini.
Moriana's mother mentioned she could not afford to live there but Moriana had an uncle who did. Kutina allowed Moriana to stay with her brother Hutaz who was a successful carpenter. Hutaz offered to teach Moriana carpentry since it was a well-paying profession for commoners, and he said it could always be something to fall back on. Kutina was against the idea, but Moriana still allowed her uncle to train her without the knowledge of her mother. Moriana continued to grow into more and more of a tomboy as she performed well in school overall but did not quite meet her mother's standards.
Moriana had an A- average when her mother wanted her to have an A+ average. Moriana explained that the pressures of living in a big city made it more difficult to adjust although she honestly managed herself fine in the city. Hutaz admitted to Moriana that she picked up the city life faster than he initially did, and Moriana informed her mother that she was set to become a nurse after graduation. The nursing field was a decent one but was still not as respected as the leadership positions offered to nobility. Kutina was simply happy her daughter was making a good living and informed her that she could always be a librarian which was a lucrative and peaceful occupation for commoners.
About three years before Zuko's discovery of Aang, the city Yegini was annexed by the Fire Nation. Soldiers and tanks rolled into Moriana's town as her worst nightmare became a reality. Moriana was forced to follow several harsh rules and Hutaz became subject to the city-wide curfews enforced by the Fire Nation military. Taxes were increased to make up for the cost of the Fire Nation's conquest of the territory. Soldiers were particularly brutal to citizens that did not pay their debts. Hutaz described the invaders as a "big fancy gang".
Moriana was inspired by revolutionaries who were protesting against the Fire Nation occupiers and sabotaging their efforts. Hutaz noticed some of Moriana's new friends were militant. Hutaz discouraged Moriana from communicating with such people and threatened to send her back home. Moriana pointed out that the Fire Nation troops blocked the border and there was no easy way to cross it without being a rebel. Hutaz asked Moriana to promise him she would never join the revolution efforts, but the teen said she could not promise him that.

Moriana and Tyson in their battle armor.
At 16, Moriana joined the United Way movement shortly after meeting the earthbender Tyson and the waterbender Jarue. Jarue was the first waterbender she had ever met, and she was shocked he traveled to another nation just to support people against a common enemy. Tyson initially wasn't in the United Way and was instead trying to find a way to get out of a gang called the Green Hangers. This conflict created a strong bond between the trio, as Jarue acted as an anchor for the new set of cronies.
For awhile Moriana's identity was not discovered by authorities and she managed to finish high school. Hutaz pushed Moriana to work, and she eventually landed a medical job. Within 2 weeks of working, Moriana's identity was discovered by police. A pair of officers tried to detain her, but Moriana managed to get away from them and linked up with her friends Jarue and Tyson.
Together, they managed to cause great damage to the troops in the city but throughout the Hundred Year War, they were unable to free it. The trio would eventually be run out of town. Moriana saw Hutaz who apologized to her, but Moriana assured him there was no reason to apologize. Moriana asserted Hutaz was a great uncle and mentor before fleeing the scene. For the rest of the war, Moriana fought against the Fire Nation in a series of fronts.
Skills
Moriana learned to fight espionage, guerrilla warfare, and directly.