Unstoppable (!Invincible!OC x !Female!Reader)

Within the Grayson household, Omni-Man stood as Earth's greatest protector, Debbie Grayson as the steady heart of the family, their son Invincible growing up beneath the shadow of greatness. Then there was Y/n.
The neighborhood kids spoke her name with admiration, teachers praised her brilliance, she had skipped ahead, sitting in classrooms beside her older brother. But it wasn't just her intelligence that set her apart-it was what came next. While Mark waited years for his powers to emerge, her's arrived early-at only 8 years old. Nolan took notice immediately. Mark loved her, truly. But somewhere deep down, there was something else too-envy, as his little sister soared ahead of him in more ways than one. When Mark's powers finally came in, it felt like everything had fallen into place. Y/n was ecstatic-finally, someone who could keep up with her, someone she didn't have to hold back for.
But that happiness had only ever been fragile. The day Omni-Man revealed who he truly was, the world didn't just change-it bled. Cities trembled, lives were erased, the man they called father was torn apart in the most brutal way imaginable. Y/n saw it all. The wake of that destruction, something inside her broke beyond repair.
Where Mark endured, Y/n unraveled.
Mark could do nothing but watch as his little sister, the one who'd always been ahead, began to fall behind. The Viltrumite Empire loomed closer. New threats rose from every corner, demanding strength, demanding resilience.
The GDA was already watching, demanding more from the girl whose abilities made her impossible to ignore. As Y/n's speed begins to eclipse even the mightiest of Viltrumites, the line between hero & something far more dangerous begins to blur. Will there be anything left of her to save?