Hikaru Shiina

Hikaru is a ribers, a synthetic organism that can adopt the appearance of other living beings. When Tsubasa first confronts a maguar, she accidentally strikes and breaks a container holding such ribers, who makes contact with her and fuses with her to become a teenage-like figure (some sort of combat suit) which then defeats the maguar. After the battle, the ribers unfuses from Tsubasa and adopts her former host's human appearance, thus becoming Tsubasa's "twin" of sorts.