Mia turned into gold due to the pendant's curse.
When the two were just young children, Erik and Mia were abandoned in the snowfield near Sniflheim and were taken in by vikings who forced the pair of siblings into servitude. One day while out on a raid, Erik found the pirate king's pendant and gave it to Mia as a birthday gift. She wishes that he would have brought her the Red Orb of Heliodor instead, but treasured his present in secret. Erik said it was sure to bring gold to those who wore it, thinking it was fitting for her personality. The two then discovered that the pendant had the ability to turn objects into gold, with Mia turning a copper coin into a gold one.
Mia realised just how valuable the necklace was, declaring it to be the best present ever. Not long after, Erik found their hideout filled with different objects that Mia has turned into gold, including a seagull that he had seen earlier. He was horrified at her actions and the two got into an argument. Mia agreed she had gone too far and attempted to take off the necklace, but there was no way of removing it. It began to glow and Mia started turning into gold herself in front of her brother's eyes. Erik realised there was nothing he could do to help her as his sister pleaded for help. Erik then abandoned the hideout to try to forget about his past and his actions. On his travels, he found out that the pendant was actually a cursed relic. Erik then threw himself into any adventure he could and became a thief. He eventually encountered someone calling himself the Seer, who told Erik to seek out the Red Orb and meet the Luminary. If he helped out the Luminary, he would be forgiven for his actions.
Mia using the power of the pendant to transform into Gyldygga.
After the fall of Yggdrasil, Mordegon took advantage of Mia's despair and loneliness and turned her into Gyldygga, one of his Spectral Sentinels, and removed the effects of the gold curse from her. Erik recounted his past to the Luminary and the others and they journeyed to the Gyldenhal. There, the group confronted Mia, who was behind the Gold Fever that was plaguing the people of Sniflheim and the Vikings. With the power of the pendant, she became a powerful monster that the party faced in battle. After a grueling fight, Mia began to lose control of the power granted to her by Mordegon, with golden tendrils sprouting uncontrollably from her and threatening to unleash the Gold Fever upon the rest of Erdrea.
Erik then leaps into action to save his younger sister, his body beginning to turn into gold in the process. Mia then tearfully declares that she doesn't need gold or treasure anymore, wishing that they could go back to the way things were before when all they had was each other. As her tears fall on the necklace, it shatters into pieces and the gold curse is lifted. The party then receives the Yellow Orb after the ordeal and Mia is taken to Sniflheim so that she can recover.
In the postgame, after the Luminary decides to go into the past, the group can pay a visit to Erik and Mia's hideout in the Sniflheim Region where Mia's gold statue is still standing. With the power of the Sword of Light, the Luminary is able to lift the curse from the pendant and return Mia to normal. Mia forgives Erik for everything that has happened, fulfilling the Seer's prophecy to the thief. Now that the curse is broken, the pirate king's pendant has lost its ability to turn objects into gold and Mia decides to entrust it the Luminary since it's worthless to her. She says that she expects the necklace back someday since it's still hers, but doesn't mind if it gets lost and asks him to look after her brother. The pendant can then be equipped by Erik as an accessory.
