The only girl of the team. 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 the 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 subjects, the only people who truly understand Kei. With them she finally learns true friendship and teamwork. Kei and Hayato grow closer over the course of the series, and as of the epilogue, they have apparently been in a relationship for some time.
