Mia

Mia, a 17-year-old Mercury Adept from the wintry town of Imil, is one of the last living descendants of the Mercury Clan. Mia is a gentle, caring young woman with long, flowing blue hair characteristic of Mercury tribesmen. She acts as a healer to the party in both games.

Background
Mia's father had previously held Alex as his apprentice (in the English translation, Alex was mistakenly called Mia's apprentice), and as the custodians of the Mercury Clan their sworn responsibilities were to live as the healers of the populace and to ensure that the Mercury Lighthouse near town is never activated. Mia, of course, never suspects Alex's hidden motives for self-gain, and she is left confused when Alex leaves Imil on his own, in effect abandoning her.

In Golden Sun
Mia's life and destiny change completely when the warrior Isaac arrives in Imil in pursuit of Saturos to prevent his band from activating the Lighthouses and returning Alchemy to the world. Mia joins Isaac in hastily climbing to the top of Mercury Lighthouse, where to Mia's supreme horror the Mercury Beacon has been lit by none other than Alex, revealed to be in league with the unusual and menacing Saturos and Menardi. Alex explains that in lighting Mercury he has freed the first part of a great power that has long been sealed away, a power that he obviously admires, and Mia in response accuses Alex of having gone mad in betraying not just their charge of duty but her as well. After Alex bids her farewell and leaves with Saturos, Mia vows not to let Alex get away with this and accepts Isaac's invitation to join his quest to stop Saturos and Alex. Mia becomes the designated healing figure to Isaac's party in their journey from then on.

In Golden Sun: The Lost Age
Isaac and Mia do not encounter Alex again for the duration of their journey across Weyard, and in fact both realize later on that the return of Alchemy is actually a necessity for the welfare of the world. However, at the end of their journey at Mars Lighthouse, the Wise One reveals that both Isaac's party and Saturos' have been played for fools from the start; Alex manipulated the objectives of every individual involved in this chain of events so that when Alchemy does return to Weyard, Alex will be at the center of the process and hoard ultimate power for himself. Mia is supremely mortified by her clan mate's base tactic for self-gain. Later, when the Adepts slay the Wise One's Doom Dragon creation and realize that they destroyed their own parents, Mia is heard voicing that she will never forgive Alex for committing these irreversible sins. Right afterwards, however, when activating Mars miraculously revives the parents, Mia returns to her serene disposition as they return to Vale and discover that the town was destroyed but all the townspeople are safe. Alex turns up missing as well.

Fan influence
Fan fiction often depicts Mia as Isaac's "love interest", so a lot of fiction about this relationship, called Mudshipping, has been penned.