Double Life

At thirteen, she dreams about being born.

At eighteen, she dreams about being a little girl, discovering she has a vague quirk where she lives another life when she sleeps but forgets it soon after she wakes up.

At twenty-four, she gets in a car accident and falls into a week-long coma. She dreams about being a seven-year-old girl in another world who has a week of insomnia.

When she's sent home from the hospital, she wakes up on the other side of her consciousness to find that she can remember her dreams for the first time, and she can't tell which one is reality. All she knows is that in one, she's watching her dreams reflected in an anime. In the other, she's a little girl, and her best friend, Izuku Midoriya, is very real and likely to get himself killed trying to be a hero.
If the anime in her adult-self-dream foretells the future, how can she be sure not to screw up the timeline so her friend can become the hero who saves the world? If she hasn't already, that is. And if she dies in this world, will her other self also die?

She's not trying to be a hero. She's just trying not to have a nightmare.