Sia is the protagonist of the Game Boy Advance game Lady Sia. In it she is the queen of Myriade, which is one of the four continents in this game; the other continents are Athorre, a unnamed continent, and Callyge.
One day Onimen the Warlock finds ancient magic in the continent of Callyge and with it he created the T'soas, which were half human and half beast creatures, to fight for him. Onimen attacks Athorre first, since that continent only inhabitted simple humans it was easier for him to take down the weak first. Then word spreads to the other two continents, their realms, and their belonging rulers.
Sia contacts the leaders of the other realms left and they decide to meet in her castle. In their meeting, Sia tried to persuade the council to help her on a quest to defeat Onimen and save Athorre. Unluckily she fails to persuade them, suddenly Barthes (Sia's advisor) informs her that the kingdom is under attack and the T'soas are heading to the castle. Sia decides to settle it down but it was too late she was take prisoner, her jade sword and family ring were stolen, and she was put in a cell in the Atthore castle. Meanwhile Barthes told the leaders Sia was disgusted by them, that she withdrew from the alliance and so that was the reason she didn't return.
In the cell she meets a peculiar cloaked man, he decides to free Sia but before letting her take off he gives her information and advice. Sia then out of the cell looks for a way out of the castle, she finds a way out through a rooftop. As she is carefully trying to get out of the castle she notices a griffin who's chained up, Sia frees the griffin, the grateful creature decides to give Sia a ride wherever she wants to go. The young queen decides to retreive her jade sword and family ring before saving her kingdom. After getting her stuff back Sia decides to visit the rulers of the other realms to see if they had changed their mind and help her after all. When she gets there they mention to her what Barthes had told them, Sia felt betrayed, but this time Sia managed to get the rulers to help her out.
Then Sia goes to Myriade, the kingdom was completely take over by T'soas. In this place Sia encounters one of Onimen's most powerful minions "Fox Lady", in order to gain Myriade back Sia has to defeat the villainess and then get prepared to face and defeat Onimen.