Kotsutsubo (movie, 2012)

Eri (Matsubara) is a high school student who is anonymous unlike her friend Mitsuko (Yokoyama) who is the target of amorous advances from their teacher, Ichida (Tsubouchi). Eri comes across a novel way to protect Mitsuko: find a cursed funerary urn that contains ashes reputed to cause death and give said ashes to teacher.