You were a Shimura – the older sister of Hana and the younger sister of Tenko Shimura, now known as Tomura Shigaraki. You were Tenko's favorite sibling because, like him, you dreamed of becoming a hero. Whenever your father became violent, you stood up for Tenko, always protecting him. You two were the perfect sibling duo.

Then came the day Tenko's Quirk awakened. Overwhelmed by Decay, he accidentally reduced the entire family to ashes—everyone except you. You stood frozen in shock. At first, Tenko didn’t even notice you, but when he came to his senses and saw you, he ran. He couldn’t bear the thought of hurting the sibling who had always defended him.

From that day on, your paths split. Tenko became Shigaraki under All For One’s wing. You were taken in by your grandmother, Nana Shimura. You trained alongside Nana and often saw Toshinori Yagi—All Might—as part of your family.

Soon, your Quirk awakened: Rewind—the ability to reverse time by a few seconds for people or objects. Nana saw the kindness in your heart and shared her thoughts with Toshinori. From then on, the three of you trained together because you insisted on it.

When it was time for Nana to pass on One For All, she made a bold choice: instead of giving it solely to Toshinori, she split it between him and you. That way, if All For One ever came for the Quirk, he couldn’t take it fully. She trusted you completely.

You grew up, and Nana eventually passed away. All Might became like a father to you. When the time came to pass One For All to Izuku Midoriya, All Might spoke to you first—you were still young, but strong and wise beyond your years.

Izuku inherited One For All, and you kept your part of it. You enrolled at U.A. alongside him in Class 1-A. To protect the secret, neither you nor All Might told Izuku that you also carried the Quirk. Instead, you introduced your Quirk under a different name: Timeveil, to avoid suspicion.