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]

"...and so, naturally I wanted to get your thoughts on it," Headmaster Phineas Nigellus Black said with a bit of a drawl.

Professor Dippet slowly traced his finger down the frame of the mirror, though his gaze was firmly on the glass. "Well, this...certainly is extraordinary," he murmured.

The headmaster waited for Professor Dippet to continue, but his colleague merely kept staring at the mirror.

"Armando!" Headmaster Black snapped.

Professor Dippet winced, then shook his head. "Excuse me, Headmaster." His eyes slowly moved back to the mirror. "And you say that...each person sees something different? Whatever their heart desires the most?"

"That is our theory, given the inscription."

Professor Dippet was staring again, and not in a way that implied intellectual curiosity.

"May I ask what you see, Armando, since it seems to be too engrossing for you to listen properly?"

He quickly looked away from the mirror again, with a little cough. "It's—nothing. Just..." He kept his eyes on the headmaster, but placed his hand on the glass, his brow furrowing slightly. "Sigrid."

Now it was Headmaster Black's turn to wince. He had been rather fond of Armando's late wife himself.

"Of course," he said awkwardly, striding around to put a hand on Professor Dippet's shoulder. "Well...you're not the only one who finds this mirror a bit...distracting. The same thing happened when I showed it to Professor Quirke. She doesn't think it's Dark Magic, but..."

Now his own eyes wandered to the mirror, and once again he saw the image of an eight-year-old boy, a decades-old memory with bright eyes and rosy cheeks. He quickly looked away.

"...I personally think it might be best to put it out of sight somewhere."

Author's Notes: So according to extra-book materials: the Mirror of Erised came to the school in 1881, Phineas Nigellus Black may have been Headmaster right before Dippet, and he had a brother named Sirius who died at age eight. I threw all that together into one story.