Sabitsuki is the main character of .flow, who is controlled by the player. Much like the protagonists of Yume Nikki and Yume 2kki, she spends the game wandering around her mental landscape and collecting a multitude of effects. Similarly, not much is explained about her past, or about the things she sees in her dreams.
(From .flow Wiki article)
Her distinctive characteristics are "bedhead" white hair, fair/pale skin, red eyes and being left-handed. She normally wears a white skirt, a violet/lilac sleeveless shirt or sleeveless turtleneck and a pair of brown leather shoes.