Sleeping Cold

The captain of squad 10, Toshirou Hitsugaya is feeling restless. Going for a walk to soothe his unease, he stumbles upon an odd spiritual pressure nearby. Racing towards it, he finds a young girl facing off with a Hollow. Before stepping in, he sees her weapon of choice. A zanpukuto.
Uta Kazume has roamed the Soul Society for many years, staying the same height though, to her annoyance. With nothing but the strange voice in her head, and her ghoulish memories for company, she trains with the sword that had appeared when she was attacked by hollows. Guided by the voice in he head, she fights hollows in honor of the friends she lost that terrible night.
Toshirou knows to take her back to the Seireitei, especially since she isn't a soul reaper, yet possesses a zanpukuto. He soon finds it odd, however, that she hardly shows any skin. Her past is a mystery, one he would like to know the answer to.

What happened in Uta's past that has her waking up screaming? What is the connection with Cherry Blossums, and who is the voice in her head?