Toko Fukawa

She has the title Ultimate Writing Prodigy and she suffers from dissociative identity disorder. Her other personality comes out when she sneezes, or upon seeing blood (which also makes her faint prior). That other personality is known as Genocide Jack (also known as Genocide Jill or, in Japan, Genocider Syo, among those who aren't aware of her gender) who has the title Ultimate Murderous Fiend.