Melia is one of the most important characters to join Shulk's party This is due to her being the first offensive mage of the game, providing a new way of defeating enemies and another ranged attacker other than Sharla.
Melia is the Daugther of Sorean, the current emperor of Alcamoth. She has an Elder brother who's name is Kallian. She is the second in line to inherit the throne of the City, and looks more like a Hom than a High Entia. The reason behind this is due to a breeding program past emperors started in order to ensure the race survived if Zanza was ever freed from his prison on top of the Bionis Head.
 Meeting Shulk
The party meets Melia for the first time, unconscious in a clearing in Makna Forest. Sharla needs pure ether crystals to heal the girl, who was suffering from ether depletion as a result of being attacked by a Leone Telethia.
While Shulk was off to get those pure ether crystals, he is attacked by Puera Telethia, the offspring of the Telethia that attacked Melia. It is revealed here that Telethia are capable of reading someone's mind, rendering Shulk's visions useless. Alvis unlocks a new Mondado Art here, the Monado Purge. Reyn finds Shulk after the battle, with both returning to the group.
Sharla successfully revives Melia with those ether crystals. However she is startled by Shulk and slaps him! At the time Melia declines to explain her reasons for being in Makna Forest, but to return the favor she leads them to Frontier Village. Upon mentioning the battle that he had with the Telethia, Melia is shocked, but refuses to believe that Shulk is capable of seeing into the future.
Only by defeating the Telethia and avenging her fallen comrades will she truly believe in Shulk's power. As a result, she'll really join the group as they continue to Eryth Sea.
 Melia's Ascension
During the events of Alcamoth we learn that not everybody is happy. She is an heiress to the throne, set to perform a test inside the High Entia Tomb as a means of proving her worth. While she is performing her personal test the party learns that there is a set up inside the Catacombs to kill her, ensuring that her older brother takes the throne (since the political situation hints heavily that she will be the one inheriting the seat from her father). Shulk and company successfully reach Melia in time, stopping Tyrea from killing Melia and defeating an accompanying Solidum Telethia, foiling the plot of the Emperor's first consort.
The forefathers tell her that she is indeed worthy of inheriting the throne (this is also because she is 80% Hom and 20% High Entia since she is one of the few immune to Zanza's wave of transformation).
After the events of Galahad Fortress the group is separated into three smaller groups. Melia lands with Riki and Dunban, as the three of them have to find where the others landed and reunite with the group.