Disclaimer and notes: I don't own Detective Conan, I don't own Magic Kaito, and I certainly don't own the quote from one of the Lupin vs. Holmes books. Setting is post-series. It was originally supposed to be a comedy piece called "The Artist and the Critic: A Love Story", in which there would be no pairings (despite the title) other than maybe Shinichi x mysteries and Kid x stealing. I don't know what happened.
"We may talk, shake hands, nod to each other, but the fence remains. You will always be Sherlock Holmes, the Detective, and I, Arsène Lupin, the Gentleman Burglar." -Maurice LeBlanc
"Looks just like the real thing, doesn't it?"
Shinichi glanced to the right, where Ran stood, bending over to inspect a large yellow jewel enclosed in a display case. "It is the real thing," Shinichi pointed out, glancing at the jewel. "That's why the museum's security personnel are here, and the police, and the former Kid Task Force, and your father, and me."
Ran straightened and smiled at him. "I don't mean the jewel."
"Oh," Shinichi said, shrugging the comment off. Then, a thought struck him... "Oh."
"Walk with me for a while," Kid said in Ran's voice, waltzing away from the display towards another part of the museum. Shinichi hesitated, but followed after him anyway. Kid wove a path through display cases and hallways until they reached a room filled with paintings. His pace slowed as he walked around the room, pausing briefly to admire one of the paintings, before his interest in the room passed. Shinichi followed him out of the room, and they entered a moonlit hallway.
"I thought you retired," Shinichi stated.
"I got bored," Kid replied. He stopped walking, his back to Shinichi.
"So are you ever going to tell me what you're looking for?"
Kid spun to face Shinichi, his hands behind his back. "And ruin your fun?" He smiled. "My dear detective, I wouldn't dream of spoiling that surprise. I'll be gracious enough to give you a clue, though." With a flourish, Kid produced the yellow jewel he'd been inspecting earlier. He held the jewel up in the moonlight. "The moon tells me what I need to know."
"When did you...?" Shinichi asked, tensing.
"I wouldn't dream of spoiling that surprise, either. I'm sure you can figure out how I got it, and when. After all, you're my number one critic."
Shinichi relaxed. "I should be arresting you, you know."
"I'm retired." Kid tossed the jewel up and swiped it as it began its descent. "Besides, it'll be back before they even know it's missing, and then whatever sorry excuse for a thief that's coming for it can test his luck, and you can arrest him."
"Not what you're looking for, then?"
"No. Not what I'm looking for."
"Hand it over. I'll tell them I put a fake in the case as a precaution."
Kid tossed the jewel to Shinichi, who caught it easily. "You're a good guy, detective."
"You're not so bad yourself, thief," Shinichi replied. "But I really wish you'd stop posing as Ran; it's getting disturbing."
Kid grinned. "It's fun to tease you like this, though!" The grin faded, and he looked upwards, gazing at the moon through the skylights. "I don't know how else to approach you. Who should I be? Mouri is too old. Sonoko is too annoying. Heiji is too far away. Ran is the only one who fits."
"Why don't you be yourself?"
Kid looked back at Shinichi in surprise. A soft smile crept onto his face, not at all like the cocky smirks or mischievous grins that Shinichi was used to Kid wearing. He thought the smile looked rather lonely. "If I were myself, you wouldn't recognize me."
"I could learn to."
The sadness quickly faded from the smile, replaced by something else that Shinichi couldn't quite place. "Well, detective, I must be off. Give my regards to Ran! Oh, and you may want to bring her here some time; she was very disappointed when you told her she couldn't come tonight."
"When I what?"
Kid's grin was more than enough of an explanation. He turned and continued down the hall.
"No flashy exit?" Shinichi asked.
"I'm retired," Kid said before disappearing into the shadows.
Shinichi stood in front of a large painting of a magician in white. Kid had looked at this picture the day that a would-be kaitou attempted to steal a jewel, and he found himself drawn to it for that reason.
Ran was on the other side of the room, happily admiring the collection of paintings the museum held. Shinichi was fairly sure that Ran had looked at nearly every painting already; he, on the other hand, hadn't moved from the magician and his doves.
"Looks just like the real thing, doesn't it?" a voice asked. His head snapped to the left, where there stood a boy his age, with messy brown hair and blue eyes.
"Oh, right. The painting."
"This one's a reproduction; my family owns the original."
Shinichi glanced at the information plate, which stated the painting was of the famous magician, Kuroba Toichi. "Are you a fan of Kuroba?"
"Something like that," the boy said.
Shinichi studied the painting in silence for a few minutes. "It's a good painting," he eventually said, "even if it's just a copy."
"Are you an art critic?"
Shinichi smiled, remembering how Kid had called detectives critics of a kaitou's artistry. "Something like that," he concluded.
The boy grinned widely; Shinichi's answer had evidently pleased him. He was about to say something else when a wild-haired girl approached him.
"Kaito, are you ready to go? Dad's finished talking to the curator."
"I'll be right behind you," the boy said to her. She nodded and started out of the room. He turned back to the painting. "This is the real thing," he said softly.
"But you said..."
Kaito smiled at Shinichi. "I don't mean the painting," he said before following the girl.
"Oh..." Shinichi said, watching him leave. "Oh."
Shinichi never met Kaito again. He did, however, meet a certain thief with a tendency to dress as Ran.