Seo Ji-yeon was born in Daegu, South Korea. She had a happy family. They weren't rich, but they weren't poor either. They were financially stable and lived well. Ji-Yeon had good grades and maintained it well. Around Ji-Yeon's twenties, she was studying to become a surgeon in the medical field. Once she graduated and became a doctor, she worked at a hospital and did surgeries for people. She was good at what she did and saved lives.
One day she had to do a surgery on a man who was shot. Thankfully she saved him. This man was attracted to her and wanted to start seeing her. So he would purposely end up injuring himself and he would always go to that hospital. One day, he 'accidentally' cut his hand with a knife and had to go to the hospital. Thanking her for fixing it he gave her a gift card to a coffee place as a way of thanking her. But when she got home, she noticed he written his number on it. Being interested, she called him and they started dating. A few years later, they got married.
Not knowing he was a terrible person once they got married, he confessed that he experimented on people for powers and such. She then found out that he only liked her so she could have children for him to experiment on. When she was pregnant with Aria, he injected something into her blood which he injected into Desdemona one, causing her to become a Metamorphigaus. When Aria was born, it almost killed Ji-Yeon. It was a miracle she lived. After living with him for so long he brainwashed Ji-Yeon, which caused her to let him experiment on people and her children, and that's how Seo Yoona was born. But like before, the man injected something into Ji-Yeon's blood, but it wasn't the same thing he injected for Aria, he injected something that would make her a lot faster than other people in anything; running, thinking, etc, and he also injected something that she could make someone unconscious and be able to heal herself. After they were born, it was confirmed the two children were healthy so he wanted to experiment with more children.
Realizing she would die if she tempted fate again and had another child, she ran away from him and sooner or later met another guy. After a while, she felt as if she could trust him and he could take care of her, so she had another child. This time the child wasn't experimented on and had a healthy child, but little did she know the father wasn't human, but also had powers.
After a few more years, forgetting her past the man found her and took her back with him. Her second husband fought for her but didn't win, as the man decided to inject something inside of him which gave him enough strength to kill someone. In the end, she was brainwashed once more and lived a "normal" family life so there two children would never find out what they've done.
When she wasn't brainwashed, she would be calm, nice, and pretty independent. She was pretty stubborn as well. When she was brainwashed and had the shot, she was a stubborn and a cold hearted person, not caring about anyone.