Parasite M

Hana-chan is is a mosquito like parasite who enters through the mouth, she then attaches her self to the victims brain, taking control. She is the only Magical Girl with the ability to communicate with humans as she talks through her host, usually with a child-like voice (ex. "sworry"). Hana-chan's transformation boosts the physical strength of her host and allows her to take total control of the body, reducing the original head to a grotesque growth while her's takes its place. Her hair also grows longer, and her flower shifts to the centre of the part in her bangs. (Source: Wikipedia)