A selection of hair dyes is seen at a store in this file photo taken in 2002. (Mainichi)

OSAKA -- An 18-year-old girl is suing Osaka Prefecture for mental anguish after her prefectural high school forced her to repeatedly dye her naturally brown hair black.

The third-year student at Osaka Prefectural Kaifukan High School in the city of Habikino filed suit for some 2.2 million yen in compensation at the Osaka District Court, and opening arguments were heard on Oct. 27.

The student has called the incident "bullying in the name of guidance." The prefecture, meanwhile, called for the suit to be dismissed.

According to the lawsuit, the student entered Kaifukan in April 2015. She had been deeply upset by being forced to dye her brown hair black by her junior high, and so her mother asked the Kaifukan administration "to take care not to let the same thing happen in high school."

However, shortly after the student entered the school, Kaifukan staff began ordering the girl to dye her hair every one to two weeks. From the second term of her second year on, she was ordered to dye her hair every four days. The student eventually developed a rash on her scalp from the repeated dying, and her hair was also badly damaged.

Furthermore, the suit states, teachers inflicted psychological damage by asking the student, "Is your hair brown because you're from a single-mother household?" And on at least one occasion, she hyperventilated and collapsed as a teacher reprimanded her, and had to be taken to a hospital by ambulance. The student was also barred from the school festival and class trips because she had brown hair.

A teacher allegedly told the plaintiff in September 2016, "If you don't dye your hair black, then don't bother coming to school," and she has not been back to class since. In April this year, Kaifukan deleted the girl's name from its rolls, and falsely informed the other students and their guardians that she had dropped out. A school representative allegedly told the girl's attorney, "Even if we had a blond foreign exchange student, we would force them to dye their hair black."

Kaifukan and the prefectural board of education's high school section told the Mainichi Shimbun that they could not comment on an ongoing court case.

A number of Osaka prefectural high schools have a "brown hair registry" -- a list of students with naturally brown hair -- to prevent mistaken disciplinary action. Critics say the registries themselves are problematic, but the prefectural board of education told the Mainichi that "it is up to each school whether to use such a system, and we are not tracking its implementation."

According to one prefectural high school that adopted such a registry about 10 years ago, when a student with natural brown hair enters the school, the shade of their hair is measured and recorded according to a numerical scale. As long as the student's hair color does not change, they are apparently safe from disciplinary action.

There are currently about 10 students in each of the school's three grades registered, and the principal told the Mainichi, "We will continue to use the system to protect the human rights of the students."

The mother of the 18-year-old Kaifukan student in the mental anguish suit has stated that she asked to use the brown hair registry if the school had one. However, Kaifukan does not use the registry system.

Some Tokyo metropolitan high schools also issue "brown hair certificates" to students with naturally brown locks.