Aoi is a teenage girl who worked for the Immigration Bureau of Japan as one of their top agents before helping save Eris. When the Immigration Bureau orders her to "dispose" of Eris and Kio, she chooses instead to save Eris so she wouldn't lose the one person (Kio) who made her feel like an ordinary girl. She has an ability called "Aport" which allows her to teleport anything to her (usually guns) within 50m of her, and because of this bizarre power, she was subsequently abandoned by her parents at a young age, leaving her to grow up on as she says "the other side of society".

Her feelings for Kio are obvious to everyone except for Kio himself and Eris, though she has little confidence in herself to successfully pursue Kio, mostly due to her bloody past and chest size. Her greatest fear is that Kio might reject her if he ever found out the full details of her past in the Immigration Bureau.

After betraying the Immigration Bureau, Aoi begins working for the Catian Embassy as its Chief of Security and given two personal assitroids to help her. Aoi is an expert in all forms of firearms and proficient in the use of a powered exoskeleton, as well as having vast knowledge on military tactics and combat theory. She has the odd ability to survive any sort of attack with little to no injury, from explosions and stun rifles, to car crashes and falling of a moving train, giving her the nickname "Charmed Momoji."
Her main hobby is collecting old and obscure movies, which is also how she ended up meeting Kio.