Aina Mikage is a high school student attending Sieryuu Academy, where she resides in the school dormitory. She works part-time at Cafe Broccolo alongside her schoolmate, Asuka Tennoji, and is noted to be a shy and sweet girl.

Her background is marked by tragedy, as it is suggested that her parents were killed by a Z/X during the Black Point incident in Tokyo. This event instilled in her a deep-seated hatred for Z/X, the otherworldly creatures central to the story's conflict. Despite her gentle and reserved nature, this intense animosity becomes a core part of her character.

As the story progresses, Aina's hatred makes her vulnerable to manipulation. She eventually becomes a user of Malice, a dark power, nearly becoming a victim herself before forming a pact with a rogue Z/X. This turn leads her to temporarily oppose the main cast, including those who saved her, as her quest for revenge and her prejudice against Z/X override her initial loyalty. Her personal journey forms a central focus of the latter half of the anime's plot.

In terms of relationships, Aina harbors romantic feelings for Asuka Tennoji, who treats her kindly and often helps her with difficult tasks at the cafe. She also manages to befriend another main character, Ayase Kamiyugi. Her character development is significant, as she evolves from a seemingly insignificant childhood friend figure into a key player with a major plotline, eventually overcoming her darker impulses to find a better path.

Aina possesses no inherent supernatural abilities at the outset, but her role as a Z/X user grants her the power associated with Malice, the entity she forms a contract with. She is depicted with black hair and blue eyes.