The White Rabbit
In 1996, Severus Snape finally meets his soulmate. She's six and a half years old, doesn't speak a single word of English and has the bluest eyes Severus has ever seen.
Then he dies on the floor of the Shrieking Shack, only to awaken back in 1976.
Yet this isn't the same 1976 he remembers. Far from it. The reality Severus once knew keeps cracking around the corners.
The politics in Wizengamot don't add up.
Neither do the events in Hogwarts.
There are weird graffitis appearing on the walls all around Wizarding Britain.
And Eileen Snape? She's gone off her rocker.
Above all, there's a mysterious movement forming, an organisation that gets spoken only in soft whispers in the Slytherin common room. Rumours say they offer an alternative to those who are unwilling to serve the Dark Lord, an escape the Light side are not willing to give.
They are called the White Rabbit.
In other words:
She was eight and he was 38 when they met for the last time. She had long forgotten his face and the language he spoke, but she still remembered his voice. It sang to her soul and lulled her to sleep every night. It kept the nightmares away, most of the time. It kept her sane.
Then, fighting against all probabilities and reason, she finds him again, twenty years later. Or earlier. It depends on the perspective, really.
But that's not what matters. What matters is that she came prepared to fight.
So fight she does.