She is the only girl in the four protagonists. Unlike the others, Kei has known about her ARMS her entire life. She was raised by the bluemen, the organization that combats Egrigori and originally implanted ARMS in four teens. Kei was raised and trained as an elite soldier,but because many of the bluemen saw her as a weapon and not a person,Kei grew up extremely lonely, bitter, and even a little vicious. This all changes when Kei meets Ryo and the other ARMS subject, the only people who understand Kei.With them she finally learns true friendship and teamwork.Kei and Hayato grow closer in the series, and as of the epilogue, they have apparently been in a relationship for some time.
18 years old,much older in last episode(manga only).
Queen of Hearts.
Takatsuki Ryo(first),Shingu Hayato(later).
Akagi Katsumi(Twin Sister),Takatsuki Ryo(brother in law),Iwao(father in law),Misa(mother in law).
Dark Brown(similar to Katsumi).
Long(change to short hair cut in last episode of manga).
Aishora city,Tokyo,Japan,Gallow Bells,United States Of America(Hunting Egrigori and Save Katsumi).