The Red Orb is a quest item obtainable in Golden Sun: Dark Dawn. It is described as "A shining red sphere." As a key item, the Red Orb cannot be sold or dropped.
The item is obtainable from Emperor Unan in Tonfon after you successfully bring back Ryu Kou and Hou Ju. Unan tells the party that Arcanus requested he gives you the orb and explains the party already has one in their possession, refering to the Blue Orb. The item is used in the Yamata ruins, alongside the Blue Orb to obtain the Yellow orb, used again on the Endless Wall along side the other two orbs to open a gate so the player may continue, and finally to help set up the activation of the Apollo Lens, at which point it will permanently disappear from the inventory.