When Harry awoke, he wasn't in his room, nor was he in the hospital wing. He was in a large bed with lavish, maroon bedding and Gryffindor paraphernalia adorning every inch of the walls surrounding him.  It wasn't his room, it was a prefect’s room. Nobody else got their own bedroom like this apart from them. That meant it had to be either Ron's or...
"It's nice to see you finally awake." Hermione said as she entered the room from the en-suite bathroom beside the room.
"Herr-merr." Harry grumbled in response. All of his muscles were weak and useless, even his tongue, which felt three times bigger and didn't move when he wanted it to.
Hermione swept to his bedside and perched on the edge. She was wearing her Gryffindor jumper and a skirt.
"Try not to speak, Harry." She spoke softly to him. "That's what Madame Pomfrey said, anyway."
Harry looked at her in disbelief, wide eyed. What had happened to him? What was going on?
"Harry..." She began, holding on tightly to his hand. "...you collapsed outside charms and err..." She looked at him uncertainly. "...voided your bowels. “Not only that, but as you can probably gather, your muscles are considerably weaker than they once were. That's why you're here."
Harry looked at her with a puzzled expression.
"You're going to stay with me until Madame Pomfrey finds a cure for it." She explained. "I'm going to look after you, feed you, and care for you." She said, smiling warmly at him. "That includes...urr..." Hermione looked down awkwardly towards his crotch. "...diaper changes."

Harry's heart practically stopped in his chest.
"I know, I know you won't be too fond of it, Harry." She argued, misunderstanding why Harry's eyes were practically popping out of his head.  "But Dumbledore has given me this important task. I don't want to let him down, and I certainly don't want to let you down."

THE TWO OF THEM sat in awkward silence until it was finally broken by Hermione sniffing the air.
"Umm...Harry, I think we might have to kick off this new arrangement sooner than we originally thought.”
Harry sighed reluctantly, but in his current state could do nothing to prevent the inevitable. He instead gave out a little whimper, of excitement, not fear.
Hermione peeled back the duvet, which had been tucked in tightly beneath the mattress, revealing Harry in all his diapered glory. He was without a shirt and trousers and was wearing nothing but his yellow Hufflepuffypants diaper, which after multiple wets that had gone unnoticed by Hermione in the last few hours, had expanded to a size that was comical for her to look at. She couldn't help but let out a little giggle.
"Sorry." She said, but clearly still trying to stifle her laughter. "It's just I didn't think it would be this big."

Harry eyed her angrily as she proceeded to undo the tabs of his enormous puffy diaper that had expanded a good half a foot out from his waist. The smell of his mess was strong in Hermione's nose, but as his new carer she'd just have to learn to get used to such things. She tried to keep from wincing in disgust.
This is for Harry. She thought. This is for Harry.

Hermione undid the tabs either side of Harry's enormous diaper and peeled the soggy nappy away from his body with a squelch. Harry's cheeked flooded red as he noticed the massive erection he was sporting between his legs. He was fonder of Hermione's mothering than he originally thought. 
Hermione's eyes widened at the sight of Harry's length. She'd never seen a boy’s penis before, and found herself unable to tear her eyes away from the sheer size of it. Harry closed his eyes in embarrassment and wanted to cry. He'd never had a say in this. He'd never got to actually voice his opinion on this. Had he known that Hermione would actually be changing his diapers and getting a full on view of his throbbing dick, he might have had something to say about it.
"Well..." Hermione coughed, still not able to stop looking, "let's crack on then."

Hermione's hands moved with surprising deftness as she swept the messy, wet diaper out from underneath him and into the diaper pail beside her. She wiped his butt and cleaned (a little too thoroughly) his balls and cock. Harry's body quivered under her touch. A new Hufflepuffy was placed beneath him in record time and taped up. The dry, crinkly material felt so much more refreshing than the warm, wet mess that was occupying his diaper before.
"There," Hermione said, still blushing after trying to restrain Harry's raging erection in his diaper and after wiping his butt clean. "That's better now, isn't it?" She cooed, absentmindedly brushing his hair with her hand.

She felt herself getting a little more comfortable with him as her baby than she should be.

*

Ginny couldn't contain her foul mood. She had to do something. She had to hit something.
"This isn't fair." She hissed, "This isn't how it's supposed to be happening." She grabbed a random book off of the bookshelf beside her and launched it across the room. Cho Chang ducked, alarmed by Ginny's rapid change in mood.
"You're a Ravenclaw." She growled at Cho. "You’re meant to be smart, why didn't you see this coming?"
Cho scowled at her.
"Stop acting like this was just your plan, Ginny." Cho replied, staring Ginny down bitterly. "We both wanted this for Harry. We'll figure this out."
"What is there to figure out? The whole things ruined." She said, looking as though she might cry any moment. She brushed her long ginger hair out of her face and stared Cho dead in the eyes.
"I hit him with the curse, and it started taking effect almost immediately. I mean, he pissed himself in his potions class not ten minutes later for God's sake."
Cho nodded as Ginny relayed their plan once again, trying to pick out what else could have gone wrong.
"Then, after the muscular spell took effect and he was left with no more strength than a baby, that's when Dumbledore and McGonagall stepped in, just as expected. That's when they were supposed to designate me as Harry's carer. And then we would have had him all to ourselves.
"But of course they had to pick fucking Hermione. That fucking mudblood princess."
"I thought you liked Hermione." Cho interjected, looking at Ginny sideways.
"I put up with her, Cho. And besides, that was before she took my baby Harry away from me." Ginny's eyes were dark and full of an anger no one had ever seen in them before.
"Can't we just get him back?" Cho asked.
"It'll be practically impossible." She replied. "The spell won't only affect Harry, it'll affect her too. Before long she'll find herself with an unexplained motherly bond towards him. She'll start wanting to look after him every hour of every day, she'll even start producing milk for him."

Ginny looked at Cho mischievously.
"All we'll have to do is take Hermione out of the picture."