She is the daughter of Seo-Joon Ikari, a korean immigrant that left his home country to live with the love of his life, Ayumi Ikari. He even changed his surname to hers to really mean that he is invested in their relantionship (tecnically, in japanese his name would be ikari Seo Joon because japaneses names are inverted to western ones, where the family's name is first and the person's name is last. But i will use the western name conventions here in this story). He was a old taekwondo champion a while back but left that lif to retire and build a family with his love.
They both had a child who they both named Yasui.
Yasui lived a normal life in Japan, going to school and making friends. She was pretty adjusted to society as a whole. Not a straight A studant, but she could hold her own.
She lived a happy life, but one day a fit of rage took over her. It was a specially stressful day, with her having bombed on her math exam and then gettin yelled at by her teacher for failing that same exam. Later, she was bullied and almost spanked by the bullies, but the energy explosion scare them away from her. She exploded with some dark purple energy power. She could not control herself. After it, she passed out and one of her teachers found her and brought her to the enfermary. She almost puts the whole school she has studying in down, breaking the room she was on and making some of wall and roof fall onto her.The principal from the school has her parents coming to explain what the hell happened and why she did that. Seo Joon explains that, many generations ago, his family was cursed with, when they feel extreme rage, they get unfathomable boost on their power but they can't control themselves. They got cursed because one of their ancestors were being insolent to some evil hermit wizard, so he cursed that entire bloodline.
Yasui was mad about it, why wasn't she told and why she never saw her dad do that before. He explained that, although it is a curse, it can be controlled and the reason he didn't tell her is because he thought that maybe if he repressed enough it wouldn't be passed to her. His theory was absolutely wrong and it exploded on his face tremendously, and Seo Joon wants to make up for it.
She says to Ayumi that they must come back to his home country to train Taekwondo. It was the way that he dominated his own anger so he thought it was a good idea to train her on it.
They travel to Korea and Seo Joon makes them both travel up a mountain named Baekdu.
Yasui was already mad at her father, with the whole "not telling her that she could explode with rage" thing but she tries to remain calm.
When they both reach the top, Seo Joon train her daughter and she is surprisingly a natural. She undestood the martial art pretty quickly it even surprise the retiree. He saw the potential on her and dreamed of her continuing his legacy. First he taught her how to "control her emotions", which was actually repressing them. Never show any negative emotions that they will go away. It is the way his father taught him, after all. This essentially made Yasui a ticking time bomb who was just waiting to explode. But after he taught her how to repress her feelings, he furthered her training on Taekwondo.
After one year and a half, Yasui came back home and was somewhat better. She also had a new way of dealing with her bullies, extreme violence.
She also travelled to Korea often to go to Taekwondo tourneys, she didn't want to at first but her dad insisted it was a good idea.
She does real well on her first and actually wins in her second tournament.
She does until he is 18, where she has competied in the olympics once and is a well know martial artist who goes to taekwondo tournaments on Korea, Brazil and international tournaments.
On the tournament, she wears long taekwondo pants, a red belt on her waist thay it's really long, a bunder to keep her boobs from messing up with her fight. He also have a scar under her eye from when a match got way out of control, and giant one in her neck from she first brought her powers and a giant rubble from the school's wall went for her neck. After that recovered, she went to the training. Also a letterman jacket custom made for her.
Although she does enjoy the fighting, she sometimes feels like she didn't chose this. That she couldn't even said no. She was given a choice, sure, but when the other option is getting ostracized from society, she didn't have a option, really then.
Although her fighting style is pretty agressive, she is actually very kind and understanding individual, always going out of her way to help people have rights and using her sport influence to make people aware of social issues. She is laid back and compassionate to those around her, though she has some mismanaged anger issues and she doesn't know how to express her feelings.