Disclaimer: JK Rowling would have never written this. I never wrote Harry Potter. Consider me an unruly child doing horrible things to her stories.
NOTE: THIS IS RATED M. THERE ARE DEFINITE ADULT THEMES IN THIS PIECE. DO NOT READ IF THIS OFFENDS YOU.
Hermione gave a luxuriant stretch, unwilling to leave the warmth of her covers. She had just two weeks to go before she was due to start her usual rigorous exam study schedule and she wasn't in the mood to listen to Harry spout off theories about Malfoy and the Prince just yet. In fact, she wasn't even in the mood to read back over the week's homework. She instead summoned a muggle novel from under her mattress, a decidedly sordid work she had purchased furtively over the Easter hols, and snuggled down to read it.
Soon, she had read enough to have become slightly flushed and breathing a little more quickly than usual. She thought for a moment and decided she had time, before casting silencing and privacy charms on the curtains surrounding her four-poster. She kicked her legs over the blankets and banished the book back under the bed, before summoning and drinking an imagination potion she had modified from a Weasley's Wizarding Wheezes product and casting a series of time-released charms.
Soon she was naked, bound lightly to the four posts of her bed and imagining a very solid Mediterranean man whispering some extremely exciting things to her. It didn't take too long for the charms she had set to kick in, giving the illusion of gentle rubbing and licking, causing her to mewl softly and squirm against her bonds.
She was actually extremely proud of these charms, having had a few initial pointers from some older girls and a quick foray into the restricted section. Pieces of her other lessons had stuck, allowing greater control over duration and intensity until a few whispered words could have her at the edge of her limits for half an hour or more. Once she had even tested their efficacy in History of Magic, knowing that most of her classmates would be asleep and pay her no attention whatsoever. Apart from a curious look by Lavender Brown (who had absolutely no right to judge), she was confident no one had noticed even as she gripped her desk white-knuckled to avoid crying out.
She was shaken out of her remembrance by her spells ramping up their intensity. The charming man had been replaced by her pureblood room-mate, who was smiling at her wickedly as she tended to Hermione's growing need with an expert touch. Hermione groaned and pushed toward the image, half forgetting that her spells would take no notice whatsoever. An exhibitionist and highly curious by nature, Hermione was not unused to her imaginings being speckled with guest appearances. She closed her eyes and began rocking her hips slowly, starting to give into the spell a little more.
Several minutes later, Hermione felt the imagination potion wear off, but her charms kept going. She supposed she must have overdone it, that wasn't uncommon, but she wasn't quite done yet and wanted the extra boost. A half dose should do it. She opened her eyes to look for her wand and found that she wasn't alone anymore. She screamed, and found a long fingered hand clapped over her mouth.
When it retreated, she stammered "D-Dobby?" She knew she should be outraged, but she supposed the calm built into the potion must still be wearing off and she instead realised that there was more than just spells working on her body. "What are you, um, doing here?"
"It's Dobby's day off Miss," He replied. "And Miss seemed like she was needing some help."
Hermione opened her mouth to protest and instead let out a long moan as she was swamped by sensation. After a few moments, she was able to gasp out "Y-you don't have to" before her body convulsed again.
"But Dobby wants to; Miss. Elves is born to serve."
Hermione nodded and closed her eyes. She would have to talk to Dobby about this later, but for now all she wanted was release. She picked up her wand from where it had fallen and summoned a soothing potion. She was in no state to enjoy this as much as she knew she could. She opened her eyes long enough to down the vial then discarded it and let her eyes close again, feeling herself open up to Dobby's ministrations. After all, she hadn't been lying when she told Ginny charms could only go so far.