Bizarre Urban Legend: Slit-Mouthed Woman (2008)

Synopsis

A serial killer terrorizes a town, stabbing people on the street. The killer hasn’t been caught yet. Shiori Ayakawa, a high school girl, aspiring to be a journalist, dares to investigate the case. She stumbles upon a strange fact. A sad voice was always heard on the crime scene. It’s like a woman singing. Shiori discovers that the song is the same as an idol singer’s. The singer, Mika Shiratori, was singing it several years ago. She went missing after her promising career ended when her face was permanently scarred by an accident. People avoided Mika, leaving Mika hopeless. Losing her sanity, she slit her mouth with a knife and deformed her face horribly. Murder is her revenge on the people who betrayed her as well as the only way for her to escape from the reality. All the people who saw her ugly slit mouth were brutally murdered.