A/N: As always, I don't own the Potterverse.
kyoka suigetsu - (n.) something that is visible but cannot be touched; the subtle and profound beauty of poems that cannot be described in words; "flower in the mirror, moon on the water" [japanese]
She was used to exploring Hogwarts, but never like this. It excited her to be awake and exploring while most of the castle was asleep, thanks to the Invisibility Cloak wrapped tightly around her. An unseasonable chill hung in the air, but she embraced the cold, reveled in it. Sneaking out of her Tower late at night to rendezvous with friends was something that had become habit over the years, but tonight was something different. A few somethings were different, actually.
First, this would be the last time she would see her seventh year friends in the castle. As they prepared to graduate Hogwarts tomorrow, she wanted to spend as much time as she could with them, as she would be leaving on the Express before their ceremony would begin. Luna knew she would see them again after the festivities were complete, and intended to meet them at the old Black place for dinner the next evening, whenever it may be.
Second, unlike most of their visits to the Room of Requirement, this one would involve no studying, no books, no educational pursuits whatsoever. Tonight, the Room would provide a place for friends to just enjoy each other's company. Perhaps it would provide a roaring fire to ward off the chill, perhaps it would provide a comfy booth in a pub setting to toast the past and the future. One could never be sure about the Room until one entered, after all.
Finally, Luna knew that her boyfriend was preparing something special for her tonight, but that was all she had been able to determine. Harry was a thoughtful boy, but was usually awful at keeping secrets, so the fact that she didn't know more was both a little exciting and a touch worrying. Harry's usual idea of "special" tended to be extravagant in the extreme, given that his godfather had taught him everything he knew about showmanship.
As she approached the Room, a visible door awaited her. She smiled, knowing she was expected. The door opened, and she was only able to take a few steps inside before she was frozen in her tracks by the sight of her boyfriend surrounded by their friends. A banner hanging over his head read "For the most beautiful woman I've ever known, only the best will do." In his hand was an exquisite diamond ring. From bended knee, he offered it to her.