Aya Orihata is a synthetic human girl created by the Towa Organization, where she is known by the code name Camille. She is initially presented as a quiet and reserved middle school student who displays very little visible emotion. This lack of expression is a result of her upbringing as a manufactured being, raised without a normal family structure. Her personality begins to shift significantly after she meets Masaki Taniguchi, as she gradually starts to smile more and exhibit a devoted and caring nature.

Her motivations are deeply rooted in her unique psychological conditioning. Having been controlled by the organization, she operates under a strict internal rule that she must never be disliked by anyone and believes she has no right to fall in love. Her primary goal in her early appearances is simply to follow the orders of her handler, Spooky E, without question. However, meeting Masaki ignites a new motivation within her: the desire to experience a normal relationship and live a regular life, even as she struggles with the belief that she does not deserve such happiness.

In the story, Aya serves as a test subject for an experiment to determine if synthetic humans can produce offspring with ordinary people. To facilitate this, she is forced to seduce and have sexual relations with numerous men against her will, an experience she finds humiliating and painful. Her role is also that of an agent who performs odd jobs for Spooky E, who uses her to relieve his stress and as bait in his schemes. Despite being considered a failed synthetic human due to her lack of special abilities, she becomes a central figure in the Vs Imaginator arc as her connection to Masaki grows.

Her key relationship is with Masaki Taniguchi, the stepbrother of Nagi Kirima. Masaki is the first person to show her genuine kindness and love, and she falls in love with him in return. This relationship is the catalyst for her emotional awakening. She also shares a complex and abusive dynamic with Spooky E, her creator and handler, who views her as a disposable tool. After Spooky E is dealt with, she comes to live with and admire Nagi Kirima, looking up to her as a figure of strength.

Aya undergoes considerable development over the course of the series. She transforms from an emotionless, obedient puppet of the Towa Organization into a young woman capable of deep affection and personal desire. Her love for Masaki gives her a reason to live for the first time, prompting her to become more active in determining her own fate. Later, despite being labeled a failure, she inherits the powerful abilities of the creature Rikki Tikki Tavi, which allows her to shift from being a protected victim to a protector who confronts powerful threats. This newfound power, however, also leads to periods of mental instability and self-criticism when she faces defeat.

Regarding her abilities, Aya was initially created without any of the special powers common to other synthetic humans, which is why the organization considered her a failure. She was solely used for her biological function in breeding experiments. However, in later story arcs such as Walpurgis' Regret, she inherits the force of Rikki Tikki Tavi, gaining significant power. This ability is connected to her heart, which has been described as representing contradiction, and she eventually becomes the completed form of this power. Prior to gaining these abilities, her only unique trait was that the character Jin Asukai perceived her heart as a small but complete flower, whereas most people are seen as missing essential parts.