Requiem (слэш)

Harry Potter is miserable, angry, and trapped at Privet Drive when something inside him finally snaps.
Then magic answers.
He wakes in the Forbidden Forest not as a boy, but as a black unicorn with silver hooves, glowing green eyes, and no way to explain who he really is.
Severus Snape finds him first.
What begins as an injured magical creature being taken in by a lonely Potions Master slowly becomes something far more important to both of them. Harry, now called Hades, follows Severus everywhere, sleeps beside him, carries him through the forest, causes chaos around Hogwarts, and discovers that life as a unicorn might actually be the safest and happiest he has ever known.
Unfortunately, the Forbidden Forest is hiding something hungry.
As unicorns begin dying and strange creatures stalk the trees, Harry finds that his transformation may not have been an accident at all. His new form possesses powers no one fully understands, his connection to Voldemort has changed, and keeping his true identity hidden becomes impossible.