Shinkichi, 21, is hired as a servant by Mrs. Toyoshiga, a sought-after music teacher. Despite the considerable age difference, they become lovers. But Toyoshiga is a jealous woman who can't stand the attention her female students pay Shinkichi, particularly the young and pretty O-hisa. This consuming jealousy may be the cause of the boil that appears one day under the teacher's left eye and grows disfiguring.
“Kasane” is inspired by a famous Japanese legend that is still often performed in Kabuki theater today.