Aeris is the last descendant of the Cetra or Ancients, the original civilization of the planet.
The Cetra cared a lot about the well-being of the planet and tried desperately to cultivate the land so as not to diminish the needed planet energy.
They had special powers as well, such as the ability to have conversations with the planet and to talk to deceased souls who had returned to the planet.

2000 years ago the “Crisis of the Sky” (an alien demon who later turned out to be Jenova) appeared.
It first approached the Cetra as a friend but then deceived them and gave them an infectious virus.
Cetra who were infected by the virus went mad and transformed into monsters. But eventually a small number of surviving Cetra defeated Jenova and confined it.

Nevertheless The Cetra were doomed to became extinct.
They slowly died out, one by one, until only one woman with the name Ifalna remained.
She was later found by Dr. Gast, a scientist who used to be the head of the Shinra science department but now had left the Shinra. Dr. Gast asked the Cetra woman to help him with his research by telling him all what she knew about the Cetra and the planet.
She agreed and gradually Dr. Gast and Ifalna began to develop feelings for each. They fell in love and started to live together.

Eventually they married in secret and two years after they had started to live together, Ifalna gave birth to a girl.
10 days after their daughter’s birth they named her Aeris (kinda weird they didn’t give her a name sooner…). Dr. Gast absolutely wanted to name her Aeris because he had already that name in mind before her birth.
They were a really happy family until Hojo ruined everything (again).
When Aeris was almost three weeks old, Hojo found their residence and wanted to take Ifalna and Aeris with him for his experiment.
Dr. Gast did everything he could to not to let this happen.
He sacrificed himself for his wife and child and Ifalna was able to escape during his resistance.
She probably moved from place to place, hoping the Shinra would never be able to find her.

It’s unknown when (it could be a short period after she left her home at the Icicle Inn but also a few years later) but eventually they Shinra found her again and abducted her and Aeris.
They were brought to Hojo’s laboratory and Hojo ran experiments on them.
Ifalna tried desperately to find a way to escape from their horrible situation and one way she and Aeris succeeded in escaping the laboratory.
But she was in a very bad way, either due to Hojo’s terrible experiments on her or because of Shinra guards who fired at her during their escape from the Shinra Headquarters.

Aeris and Ifalna ended somehow up at the train station where Ifalna couldn’t take it anymore and collapsed. She knew that she was going to die and handed Holy – the ultimate white materia that had been passed down in her Cetra clan for generations – to her daughter.
She told Aeris that she had to take care that the materia never fell into hands of someone else.
Ifalna became weaker and weaker and was barley be able to comfort her crying daughter who watched her mother dying.

But then Elmyra – a woman who went to the station every day to see if her husband had returned from the war against Wutai – noticed them and ran to them. She was however too late to do something for Ifalna. Nevertheless Ifalna was glad she came because she seemed a kind-hearted woman who would take good care of Aeris. Right before she passed away, Ifalna begged Elmyra to take Aeris somewhere safe.
Elmyra hugged the child to console her and decided to take her home. Aeris and her foster mother became close very quickly.
Aeris loved to talk to Elmyra about everything, but kept her Ancient descent secret.
Both Elmyra – who had lost her husband – and Aeris – who had lost her real mother – found happiness again.

One day however the boss of the Turks, Tseng, found out where Aeris lived and went to her home.
He told Aeris that she had to return to the Shinra because they needed the help of an Ancient to find the Promised Land.
That’s how her foster mother found out about her Ancient descent.
Aeris was upset because she didn’t want to go back to the Shinra and denied that she was an Ancient.
Tseng could have forced her to come if he wanted but he felt pity for the little girl and left her house without taking her.
But from that moment the Shinra knew where she lived and was constantly after her to get her back.

Even though Aeris knew how dangerous it was for her to go outside, it didn’t keep her from going to several parts of Midgar, even to the slums which were full of danger.
Her most favorite place was the church which was the only place in Midgar where she could hear the voice of the planet and could talk to her deceased mother.
She started to plant flowers inside the church and to her surprise they had no trouble blooming there.

That’s how she became a flower girl and earned her living by selling her flowers in the streets of Midgar.
When she was about 15 or 16 years old, she had her first boyfriend, a First Class Soldier named Zack but they were never really serious. Nonetheless she was heartbroken for a while when Zack left Midgar to find a job when she was 17 but never returned to her Aeris never knew that he had actually died and thought that he had found someone else.
One day she stumbles upon a mercenary who kinda looked like her former boyfriend.
That’s when she met Cloud for the very first time in FFVII. Later in the game, she joins Avalanche and discovers Cloud is different from who she first thought he was.