Hatsune is an 11-year-old mute girl. Her mother and father garnered up a huge debt from gambling and disappeared, leaving their daughter behind.
SpoilerThe female voice that Yume heard at Hoozuki field was Hatsune doing imaginary singing in a cave. Unaware of herself, she was singing for real, and the voice echoed through the natural cave connections under the island. She regained her voice when she tried to warn Kokoro that Kuwadate was going to attack him from behind.
