Sora is a Human doctor that works in a hospital with which Mu Young is somehow affiliated. She and Mu Young are close friends and their families seem to know each other. She seems to have only recently become a full fledged doctor and is frustrated her parents are now pushing her to get married right away (they consider Mu Young a candidate though neither he, nor Sora seem romantically interested in one another).
She seems to be at least in her late 20s as Mu Young is thought to be 25 and she considers herself older than him.
Because the two of them are so close, she is willing to give him information (such as about the recent strange deaths) or do things that might otherwise get her into trouble (like take blood from their transfusion center).
She has met the Tals living with Yu Jin and helped them out while Mu Young was recovering from Leon's poison but, strangely, they did not appear to have erased her memory after those events. It's unclear what she knows or what she thinks of the things she saw and experienced during that time.