Property of the Half-Blood Prince (слэш)

Three months after the Battle of Hogwarts, Snape wakes in St Mungo’s to a scarred throat, agonising pain, and a devastating truth. He only survived Nagini’s attack because his near-death shattered a seal on his blood, reawakening his creature inheritance. Now, he is an incubus, and if he does not begin to feed, he will slowly die of starvation.
When Harry discovers the truth behind his Professor’s deteriorating health during Eighth Year, he offers himself without a second thought. But saving Snape’s life comes at a high price: The mating ritual asks for absolute submission, binding Harry in a magical contract that would make him Snape’s property through magic and law.
Horrified, Severus rejects Harry’s sacrifice, but he soon comes to realise that Harry needs the safety of a bond just as desperately as he himself.