Homura was the name given to one of two of Rukia's "children" who took her captive and erased her memories.

Homura has light green hair, while the roots appear to be bright pink. Along with that, she wears a light pink kimono with a brighter pink, down-turned, collar. She also wears a yellow cloth around her waist.

Homura helped to rid Rukia of her memories so that she could pass to be Rukia's sibling. After that failed, though, they merged together to create a destructive being, called Dark Rukia, in a process of hollowfication. Their mission is to destroy anyone that get in their way.

Powers

Flight: In the movie, she is seen floating in the air, distracting and talking to Rukia while Shizukui slashes her with his scythe.

Unnamed Ability: In the trailers it was shown that she can make a wishes, that are undoutbly granted.

Teleportation: She can teleport to places similar to Shunpo or Sonído.

(Source: Bleach Wiki)