Persona (2001)

Yuki Kawaniura and Mitsugi Ashihara are students at the private Koyokan High School. One day they receive an e-mail invitation to a "mask" party from the quiet and introverted classmate from their old middle school.
Strange things start to happen at their school, as pupils start to don masks and take on new persona's. This fashion appeals to the twin desires of anonymity and to be some else, and quickly becomes a social phenomenon.
Then pupils start to die, and so Yuki and Mitsugu begin to investigate the circumstances behide the deaths. They soon encounter a youth obsessed with making strange and beautiful masks, and are drawn into his mysterious world