When Alchemy was sealed away the Mercury Clan was designated as the sworn guardians of the Mercury Lighthouse near Imil, given the responsibility to ensure that the Lighthouse is never activated so that Alchemy's seal may be broken. In the present age, only four individuals are known to be alive: Alex, Mia, Justin and Megan. Alex breaks his bloodline's code in Golden Sun by helping Saturos light Mercury Lighthouse with the Mercury Star and travelling with him across Weyard to activate all the rest. Mia, in response to this betrayal, joins Isaac's party in pursuing Saturos and Alex.