MAGIC KAITO

Kaito Kuroba is a normal teenage student whose father died under mysterious circumstances eight years ago. Eight years later, he is made aware of his father's secret identity; a famous international criminal known as Kaito Kid, and that he was murdered by a mysterious organization because he tried to steal a gem which was also targeted by them. The goal of the organization is to find within a year the Pandora Gem, a mystical stone said to shed tears during the passing of the Volley comet (which happens once every 10,000 years): drinking these tears bestows immortality.
He vows to prevent the organization from gaining immortality, and assumes his father's thief identity as he begins his quest for the gem. His only clues as to the gem's location are that it glows red under the full moon and that it is a doublet: a gem hidden within a larger gem. Thus, it would have to be a relatively large one with a bizarre history, and always stored in a place that never receives moonlight. He thus researches and steals famous priceless gems with odd histories from incredibly well-defended areas, but returns them after the very next full moon as they are not the Pandora.