The mother of a 16-year-old girl who died of extreme weight loss after a long detention and interrogations by authorities is seeking compensation from the state in a new case of "hostage justice" in Japan.

According to the complaint, filed Wednesday in the Kobe District Court (west), the young girl was so traumatized by her 18 days of incarceration that, five months after her release, she weighed only 20 kg, before dying in December from emaciation.

"My daughter was unrecognizable when she died," said Runa's mother - a pseudonym used in the complaint - at a press conference Wednesday.

"I want to know what happened to her, and why she was arrested, detained and died," the plaintiff added.

Critics of the Japanese judicial system claim that the presumption of innocence is not always respected and that the authorities rely heavily on confessions.

According to them, suspects who choose to remain silent or deny the accusations are often subjected to long and trying pre-trial detentions, with confessions becoming de facto a condition for release — hence the term "hostage justice".

In June 2025, Runa, then an employee at a center for disabled people, was arrested on suspicion of assaulting a patient. Runa has always maintained her innocence.

The complaint alleges that she was simply trying to prevent the patient from biting another person by gently placing her hand under her chin.

It took the authorities 18 days - during which she was unable to see her family, had contact only with her lawyers and was subjected to repeated pressure to confess - to decide to drop the charges against her completely.

The family is claiming 100 million yen (approximately 540,000 euros) in damages.

During police interrogations, she was threatened with placement in a rehabilitation center and told that she would no longer be able to see her mother if she did not confess, Masahiro Sasaki, the mother's lawyer, told AFP on Thursday.

"You did it, didn't you? Now confess," an investigator allegedly said to Runa, according to Ms. Sasaki, citing a diary kept by the girl during her detention.

As a consequence of this detention, the duration of which was extended twice, Runa was diagnosed with acute stress, eating disorders and post-traumatic stress syndrome, according to the complaint.

The Kobe prosecutor's office declined to comment to AFP, stating that it had not yet received the complaint.

"Hostage justice" is regularly denounced by international human rights organizations.

An emblematic case is that of Iwao Hakamada, held for four decades on death row, whose conviction, overturned in 2024, was based in part on confessions obtained during interrogations that the Supreme Court deemed "inhumane".