Pandora Gem

The Pandora Gem (パンドラ Pandora Gem) is the target of both Kaitou Kid and the criminal organization that Snake is working for. It is supposed to grant its possessor immortality.

The name of the Pandora Gem probably comes from Pandora's Box, a Greek myth about a woman who foolishly opens a box that contains the evils of the world.

Background
According to Snake's unnamed superior in the Magic Kaito case "Blue Birthday", the Pandora Gem is a jewel hidden inside a larger jewel that will glow red under the moonlight. According to myth, if the Pandora Gem is held under the moonlight at the time of the fictional Volley Comet, which passes close to Earth every 10,000 years, then the gem will "cry". Anyone who drinks these tears will then become immortal.

Magic Kaito
Kaito Kuroba decides to become the Kaitou Kid with the intention of drawing his father's murderers into the open. It isn't until after several high-profile heists, however, that his father's murderer appears, in pursuit of the Blue Birthday sapphire.

Snake shoots Kid and takes possession of what he thinks is the Blue Birthday, but Kid survived thanks to having put the real Blue Birthday gem in his breast pocket. Snake goes to an old-fashioned mansion on the edge of the city, where a mysterious balding man with a mustache praises Snake's work, saying "This jewel could be the one he is searching for." The man then explains what the Pandora Gem is: a jewel hidden within a larger jewel that can be identified because it glows red under the moonlight and will, at the time of a comet, "cry tears of immortality". Kid reveals himself to the two men, and vows to find Pandora before they do and "smash it to bits."

In subsequent Kaitou Kid cases, notably the "Red Tear" case, in which Snake appears again, Kaito is shown to be searching for the Pandora Gem.

Detective Conan
The Pandora Gem has never been mentioned directly in Detective Conan, although Kaitou Kid has made it clear that he is looking for a particular gem as he often says he is returning a jewel "because it's not the one I'm looking for". Even though the stories of Magic Kaito and Detective Conan are set in nearly identical "fictional universes", outright magic and advanced technology well beyond that of modern times are present only in the former. Cases adapted from Magic Kaito material for the Detective Conan canon have removed references to Pandora. That makes it unlikely that Pandora, a magic gem that can grant immortality, will appear in Detective Conan's continuity.

It should be noted that in the Detective Conan manga, Kaitou Kid is rarely shown holding gems to the moonlight (to check for Pandora's doublet) outside of what is necessary for a trick. By contrast, animated Detective Conan adaptations, movies, and specials, show Kaitou Kid inspecting gems by moonlight much more often.

At this point, no direct connection has been made between Magic Kaito's Organization which is hunting for Pandora and the Detective Conan's Black Organization.

Separate from the Pandora gem, the myth of Pandora and her box has been brought up in the Big Adventure in the Eccentric Mansion case. First, Ai Haibara discourages Conan Edogawa from investigating the phone number of the boss of the Black Organization saying that the address is like "Pandora's box". Then at the end of the case, Kaitou Kid discourages Conan from investigating his true identity using the legend as an allegory.

Trivia

 * In Judeo-Christian tradition, the snake in the Garden of Eden is the reason people are no longer immortal. He convinced Adam and Eve to eat the Apple of Knowledge of Good and Evil instead of the apple of the Tree of Life. Apples represent immortality in the culture of many ancient societies, particularly ancient Greek mythology. In this vein, the Pandora gem, with its red hue, can be seen as a sort of apple.