Echo Gems are special stones in Golden Sun: Dark Dawn. These come in pairs, and they employ a mysterious effect that causes both stones to emit light whenever they are both currently possessed by a living person, regardless of how far apart the two stones and their holders are. It allows the user to determine whether a specific other person such as a loved one is still alive.
A set of Echo Gems are held by the queen of Tonfon, Lady Hinechou, and her daughter, Hou Ju. Hou Ju is captured and held prisoner at Belinsk, and later, the Grave Eclipse sows chaos and death across much of Angara; Hinechou is worried enough that she can't bear to look at the Echo Gem in her drawers, which risks telling her that Hou Ju is dead. Late in the game, Matthew and his party, looking for Ryu Kou and Hou Ju themselves, get Hinechou's Echo Gem through devious means, and pinpoint Hou Ju's location at the top of the sea, at Iceberg Outpost. After Hou Zan dies and is buried, Hou Ju dedicates her own Echo Gem to his grave before returning to Tonfon with Ryu Kou and Matthew. Afterward, Hinechou's Echo Gem may be sold for 2400 coins.