Seraphina (Gallagher) and Frank Johansson were having trouble in the baby department. Seraphina had gone through premature menopause at the age of seventeen and was unable to ever have children again despite her wishes to have one. The two had researched many different options and had decided to adopt. It took them a couple of years seeing as they were "newly wed" (At this point they had been married for only two years) in the eyes of many agencies so it was risky but finally they had settled on a baby girl from Korea. Her parent was a teen mother who's partner in crime (the teen father) had been moved to France by his family to get away from the pressures of taking care of a child, especially in a place like Korea (Eastern civilization is extremely conservative) where it was highly unacceptable to have children at an age where you should be studying and preparing for the future.
Changing her name from Byun Hana to Petal Johansson for ease to fit in with America, they gave her a stable childhood. It was a fairly basic life--public school, a few sports club, mediocre grades, etc. Both parents were also involved in the PTA and participated in many activities to help benefit the school such as fundraisers. The family was also extremely vegan. Petal generally enjoyed her life and never forgot her true origin by participating in traditional activities in Korean culture.
As time had passed, Petal had foggy dreams of the future. She had quite recently expected they were wacky fortuitous events until they became less foggier. Before long, she could dream entire scenes of herself clearing her locker or setting off to the shopping center. Sometimes they wouldn't be about herself, but her parents. She could see a bank heist in a similar bank her adoptive father had worked at. Each time she would talk about these predictions/prophecies, it sounded like nonsense to those around. This caused her to be brought to various experts and specialists at thirteen years old as her parents expected she had some kind of mental illness. Despite this, all the tests had all come back negative.
Petal soon began to not only have dreams, but flashes/visions (Think Raven in That's so Raven). She could be walking home and all of a sudden, she'd get a vision of the past or the future. She'd see herself at three years old, getting rushed to the hospital after falling down and hitting her head. She saw her parents when they had first met and when they had gotten married. She could even see her parents arguing about her and how they wish they had never gotten a crazy child.
One time, she had even seen a monster on her way back from school. Terrified out of her mind, she assumed it was a 3D animation and had pushed it out of her head. No one else was afraid, maybe she had just imagined it. Denial, denial, denial. It was better than trying to make sense of it all. It was much easier to believe she was a psycho than to think that what she saw was real considering all the other 'coincidences' were true.
All of this couldn't be explained when she told her parents in vivid detail what she had seen. They denied everything in their minds however and kept asking her to stop snooping around the house. The two refused to even try to believe it so they kept bringing her to more doctors and specialists.
Once she turned eighteen, she had a dream of a camp. It had young children and teens. In this dream she had seen sword fighting and some people doing things (using their powers) in a way she had only seen in the movies. It was practically unbelievable. Petal couldn't believe it all herself considering her dreams usually were about the past, the present, or the future. As the dreams had furthered, she was spoken to by a man. The man called himself and Apollo and told her a set of directions. It was nonsensical to do something that was told to her in a dream and yet she was hoping that maybe, just maybe she'd find something. Find out who she is, anything at all. Her dreams weren't something to joke around with, it had to be something. As soon as she awoke from her dream, she had told her parents there was somewhere she had to be so she could find herself. Anxious but knowing that she'd probably do it if she said no, the two let her go. The two actually secretly hoped that the child they had adopted would get rid of whatever was going on and come back to them when she was better, wherever she was going.
Gathering up all the money she needed (Support being from her parents), she had followed the directions given to her by Apollo and set her way to Camp Half Blood. It was quite a long journey but as soon as she got at the border, a vision came to her. It was Apollo telling her why she could the future and that she had powers not many had. He also told her about the mist and various other things that she had questioned her entire life. Everything she had thought was true, she had a destiny.
As Apollo had told her more through her visions, she had found herself in the Oracle's cave. There Petal was made the new apprentice oracle of Dodona by Apollo.