If Harry had to explain how the situation came to be, he'd admit the whole thing was a bit barmy. Neville was desperately looking for an excuse to get away from Longbottom Manor for a year or four, so he'd managed to convince his grandmother that buying a large flat was a great way to earn money with the Longbottom Vault. The absurdly low price didn't hurt his cause, as the economy hadn't quite recovered from the fear of the Death Eaters yet. So Neville found himself the owner of an enormous six bedroom flat just off of Diagon Alley. He'd wanted a smaller one, but Augusta saw the price on this particular one, and immediately bought it.
The place itself was relatively nice. The main floor plan was as open as it could be. There was a large communal area, with the kitchen barely tucked away off to the left. To help offset it, there was a staircase on the other side of the communal area, with a small closet in the open space it created for cleaning supplies or whatever else was needed. There were two half bathrooms downstairs as well, which was convenient since all six bedrooms had their own bathrooms as well. All the bedrooms were upstairs, aligned in a simple fashion with three on one side of the upstairs hallway and three on the other. There was a single, solitary window on the far end of the hallway, which contrasted it sharply with the huge windows that commanded the downstairs area. All in all, it was a nice bland place that could be easily adjusted to suit the needs of whomever lived there.
The first thing Neville did was move in. It was a relatively quick process for him, as he'd had seven years prior to get into the habit. The second thing he did was realize that he had way too much space to be comfortable. Since the space itself wasn't going to be reduced anytime soon, the only logical step would be to find housemates. His first owl went to Harry, who he remembered was avoiding the old Black Manor like the plague. Harry contacted Ron and Hermione (after clearing it with Neville, of course). Ginny overheard Ron talking to their mother about it, and invited herself along (without telling Neville, mind you). Everything went off without a hitch, unless you could call Molly Weasley sending nearly twenty pounds of cooked food with her children a "hitch."
So Neville was left with six bedrooms and five people. It didn't take long for Ginny to drag Luna over for a visit (one day and three hours after they moved in, to be exact), and Luna said "Living here looks like it would be a lot of fun." Ginny gave Neville an inquiring look, and, a confirming nod later, they had their sixth person.
The days went by quickly, with the sextet gradually getting used to one another's quirks. Harry took over the kitchen, Hermione put a permanent silencing charm around Ron's bedroom, and Luna had to be reminded that clothes here not optional, twice. Thankfully, Ginny was the one who caught her both times, so all of the males managed avoiding that awkward conversation.
Everything was going perfectly normal until Hermione saw Harry glancing at the cupboard under the stairs. Harry didn't notice Hermione at the time, and she pretended like she hadn't realized what he was doing. She talked to Ron that afternoon about what Harry's house had looked like when they rescued him after first year. Ron didn't make the same connections she did, and she didn't bother explaining. Instead, she went straight to Neville, who had been making tea for himself while talking to Ginny and Luna in the kitchen. Harry arrived from a grocery run not too long after, but he was quickly relegated to sitting on the couch while the other five talked.
So here Harry was, watching the (to him) silent conversation going on between his five housemates. He had no earthly idea what he'd done, and he was still a bit jarred to be told in no uncertain terms to sit on the couch until his presence was asked for. By that point, they had all congregated by the staircase. The discussion looked relatively calm, but a bit tense. That is, until Luna whispered something in Ginny's ear. Ginny snapped her wand up, and looked like she was about to destroy something until Neville's quick disarming spell caught her. She turned towards him in rage, but he appeared to say something along the lines of "this is my house," and Ginny backed down.
Luna was the main person who kept glancing at Harry while everyone else talked. She must have seen something in his body language, because she practically stalked over to him. Her eyes weren't distant at all at that particular moment, and Harry found the sight both mesmerizing and terrifying. She stopped a few feet from him. "I know that you are a kind person, Harry Potter, but if you one day wish to retaliate against your relatives for the awful things they did to you, I would be glad to help you transfigure their dead bodies into bones and feed them to a dragon." With her piece said, she spun around and walked towards one of the bathrooms.
"Bloody hell." Ron said what they were all thinking. Apparently, someone had taken down the privacy charm.
"Quit staring at her bum, Ronald." Hermione said as she swatted him on the head.
"Oy, woman! I'm not!"
"I don't mind when Ronald stares at my butt, Hermione." Luna returned over her shoulder.
Hermione sputtered for a moment as Luna entered the bathroom, "It's not proper!"
"It's not your butt, Hermione." Luna rejoined.
Hermione made a huffing noise before she turned back to the others. "What should we do about the cupboard?"
Ginny muttered, "I still say we blow up the bloody thing." That explained her reaction earlier.
"You are not allowed to blow up my bloody cupboard, Ginny..." Neville tiredly responded.
"Why don't we just turn it into something else?" Luna re-entered the conversation.
"Because I want to blow it up." Ginny replied.
"You shouldn't blame the cupboard for your sexual frustrations, Ginerva." Ginny turned bright red, which offset her brother's slightly greenish tinge. Neville also turned bright red, while Hermione just looked affronted. Ron caught Neville's reaction, but Luna again spoke before he could, "Ronald, you know that Neville wouldn't take advantage of Ginny. If anything, it would be the other way around."
Ron looked pensive for a moment, before he just settled into a resigned sigh. Ginny muttered something under her breath that Harry didn't catch. Neville's responding mutter was a bit louder, but Harry still didn't hear him. Hermione looked so affronted by it that she nearly appeared betrayed, but Ginny just grabbed Neville and snogged him in response. After they came up for air, Neville said, "That works, too."
Ron had a look on his face that probably mirrored Harry's own. Hermione gave up being affronted for the resigned, disapproving look similar to Ron's from earlier. "Honestly!"
Luna just clapped her hands in excitement. "I was hoping they would do that."
"Why?" Ron asked.
"They'd been looking at each other all last year, Ronald." Luna replied, "Hermione?"
"Yes?"
"Shall we transfigure the cupboard area into a small bookcase?"
Hermione's eyes lit up. "That's a brilliant idea!"
"Harry Potter, could you stand up and turn around please?"
"Um. Yeah." Harry said while he obeyed. "Why?"
"Hermione likes staring at your butt, but she's afraid to ask. I'm just doing it for her."
Harry heard Hermione sputter out a denial, and Ron make a groan of unease. "You can join him, Ronald."
"Huh? Why?"
"Because Hermione will yell at you if you stare at my butt. I think I can get away with staring at yours, though."
Harry felt and heard Ron's heavy footsteps walking up next to him. "It's a nice wall, isn't it?" Ron remarked.
"It's very nice." Harry returned with a smirk.
"Luna, that was a spectacular idea." Ginny joined the conversation again. She was likely talking about the mini-library. "Neville, go join Harry and Ron." Or, perhaps not.
Neville practically skipped over to the other two.
"We're discussing the niceness of your wall, Neville." Ron restarted the conversation.
Neville continued happily staring at the wall for a moment before he snapped out of it. "Huh? Sorry, what?"
"Ron and I were discussing the niceness of your wall." Harry helpfully said.
"Narwhals are wonderful creatures." Luna sagely added.
Yep. It was going to be a fun year.