>>3941422Spoilers ahead of course:
Io, combined with you, is able to restore the memories of Revenents. When a Revenent dies and is brought back, a portion of their memory is erased. Sometimes these memories will scatter in the form of vestiges, ordinarily touching a vestige will kill you but the player character has a special ability that allows them to hold them. If you bring a vestige to her, she can use your power to peer into the memory and give it back to its owner. This also means that if she wants to, she can look through your memories.
Because over time she finds her purpose. Like you, at the start of the game she has no memory. It's revealed through the memories of Leda that she's an attendant to a successor with the purpose of watching over them so they don't succumb to a violent frenzy. It's a bit more complicated than that but I'd pretty much have to explain the whole plot to elaborate more. As she learns more of who she is and why she was assigned to you, her personality solidifies more and more. She goes from meek, unassuming and weak to a strong, capable fighter who knows what her purpose in life is and she's very committed to that purpose.
