Summer after 4th year. Draco, bolstered by the Dark Lord's return, decides to get revenge on Hermione. Visiting her house, he places her parents under the Imperious and gives her this Ultimatum: Be his obedient pet, or per parents will kill themselves.
From there, the story would revolve around Draco's sexual abusing of Hermione. Not just raping her, but drugging her with potions, punishing her by letting others use her, and slowly conditioning her into a mindless sex toy.
Several scenes I would suggest:
-Doseing her with a temporary love potion and making her beg him to use her -hexing her so that he can arouse her (Vibrating underwear, make her feel like her pussy/arse is being pounded, like she's being groped, etc.) in the halls and class, tormenting her whenever. -A decent way into the year, disappear her into a hidden compartment in his trunk designed into a sex dungeon.
Things I DON'T want to read:
Vore, Scat, Waterplay, etc. Basically, the REALLY creepy shit.