Shiro was born in a middle-class family in Atlas. Her parents brought her with them to a business trip to Vale as they wanted to have a vacation after their business trip was over. Shiro's parents died in a car accident after leaving the babysitter with Shiro. She got sent to an orphanage because she had no other living relatives where she made friends with 4 other kids.
One of them, Kai, was adopted and had to move to Vacuo with his new family. Hanako, who had a crush on him and has been friends with him for a really long time was left devastated by the sudden turn of events and was depressed. Shiro and the two other boys, Takashi and Yuu tried to cheer Hanako up but nothing worked.
Takashi remembered a beautiful grove he found outside the city when he also found a way out of Vale by closely watching the guards' patrol schedule and proposed the idea of showing that to Hanako. Shiro warned them that its a bad idea as that is Grimm territory but Takashi and Yuu didn't listen to her and persuaded Hanako to go with them. Fearing for her friends' lives Shiro went with them too.
They managed to slip past the guards and made their way through the forest. They reached the grove and indeed it was really beautiful. It also seemed that their plan worked and Hanako was smiling once again. They spent some time in the grove, too much time in fact and when Shiro realised this she was nagging her friends to turn around and go back before something bad happens. They didn't listen to her as she was the type to get scared easily but her fears came true and two Beowolfs and an Ursa stepped into the grove. The group tried to run but Hanako fell, Yuu rushed to her aid but was too late and the Beowolfs mauled them to death. Shiro and Takashi ran for their lives from the Ursa that was still chasing them, Shiro was not able to run fast enough to escape and knowing this, Takashi caught the Ursa's attention by shouting at it and throwing a rock at it and led it away from her, disappearing into the forest.
Shiro ran until she reached the spot where they got out of the city and waited for Takashi to return but he never did. She ran back to the orphanage, barged into her room and cried for the rest of the day. She took all the blame on herself, thinking that it was her fault that they died, that she wasn't able to save them because of her personality. She also suffered from nightmares every night. A week later a group of huntsman found three corpses and when the police identified them they were indeed Takashi, Yuu and Hanako. They asked questions to Shiro who broke down during the interrogation but they tried again later and finally she was able to tell them everything that happened.
Shiro developed immense hatred towards Grimm and decided what carrier path she will take, to become a Huntress. Before she could do that she needed to overcome her nightmares and guilt. She figured it was her personality that was the reason things played out as they did so she completely sealed away her current one and constructed a new one, a cool, tomboy-ish, reliable and intimidating personality and changed her clothes accordingly too. It seemed that the nightmares were getting better and when she did have them she wasn't feeling as hopeless and scared as before. It came to the point where she barely had any nightmares in one year. Now she finally could focus on training.
At the age of 14 she started attending Signal Academy while she also took up jobs that made her easy money like taking dogs on walks, lawn mowing and the likes. When she turned 18 and graduated from Signal with good scores, she inherited all her parents' money. This meant that she finally could stop taking small jobs and could sustain herself from just her inheritance. She also made her combat attire around that time. She got accepted into Beacon Academy to further train to be a Huntress.