Aya Brea is the main character of the story, and right from the beginning of the game the player realizes that she is a special woman.  Aya possess different mitochondria than everyone else, which enables her to successfully go near and fight eve.  Aya's good is a direct contrast to the great evil of Eve.  On the outside, Aya is a rookie cop who has not yet gained any instinct, however she is ironically the only one on the police force who can stop Eve.  Aya's childhood was sad an lonely, as she had to spent much of her child life in foster homes due to a horrible accident involving her sister and mother.

Aya's character will become increasingly complex as you progress through the story.  She is presented with challenges and is forced to question herself many times.  Her relationship with Eve is a unique one of good and evil, mentor and pupil.  The question of Aya alliance is questioned many times.  Aya's relationship with Daniel is also unique and supportive.  Although her powers are far beyond Daniel's comprehension, he isn't afraid to kick her in the butt when necessary. Aya is truly a dynamic and round character that will change as your perception of the game  changes.  You will be forced to ask yourself many hard questions and solve many mysteries to free the mitochondria.  It is important to remember to keep your friends close, but keep your foes closer.  Good Luck Rookie!

Melissa's character is one of great depth and evil.  She is the living manifestation of the evolved mitochondria that threaten to destroy humanity.  Before she was infected with the mutated mitochondrion, she was an aspiring opera singer who had just got her big break.  But due to the evil that lives insider her, Melissa destroyed the opera hall on opening night.  She is now pure evil, and will not stop until she takes over the world.  Only one person can stop her, and that person is Aya Brea.

Aya's relationship with Eve is a unique yin-yang type relationship.  Although Aya is good, she still needs Melissa to explain to her what is happening, for Aya's mitochondria are too changing.  Melissa uses Aya as a pawn, drawing Aya to her only to destroy her.  But Melissa's arrogance may prove to be her biggest vice, for Aya is more powerful than she thinks and Eve may be defeated once and for all.