Serena appears as a ghost to the Hero fairly frequently throughout their journey. From the snippets of speech you overhear whenever she shows herself, it seems as though she is searching for someone, though it remains a mystery as to who for quite some time.
Later on in the game, the Hero learns more about Serena's life, and how it came to its tragic end. Serena was a victim of the vicious Gittish Empire.
She was just a young woman living simply in the small town of Wormwood Creek, when suddenly something fell from the sky. It was Corvus, a Celestrian that had been attacked by the mighty Barbarus in the air. Immediately she fell deeply in love with him, and cared for his wounds as best she could.
Soon after Corvus' fall, a squadron of Gittish soldiers came into town, looking for the Celestrian. While her father distracted the leader, Serena led Corvus to a secret hideout to the north where they would be safe.
For a short time the couple were left in peace, but their safety did not last long. Unexpectedly, Gittish troops gathered outside. Serena's father had betrayed their location in a desperate and selfish act to save his own life. The soldiers took Corvus and slew Serena along with her father.
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