On Friday, the family of a Sri Lankan woman who died while in Japanese immigration custody sued the government in a high-profile case that has reignited calls for system reform.

Wishma Sandamali, 33, died a year ago while being held for overstaying her visa after seeking police protection to flee an abusive relationship.

The victim had complained for several weeks of stomach pain and other symptoms, and a government investigation into her death concluded she received inadequate treatment as her health deteriorated.

She died at a facility in Nagoya's central city. Simultaneously, Sandamali's family filed a lawsuit against the national government on Friday, according to their lawyer's office, without providing further details. According to local media, the family is seeking $1.3 million in damages.

Her younger sister, who was carrying a framed photograph of Sandamali, told reporters she was expecting a long wait for more information.

"I'm very sad that we had to take legal action to find out what happened to my elder sister," she said in the Sinhala language.

"Litigation means a process that will take a few more years. That means I have to wait a few more years to find out the reason for my elder sister's death.”

"I am truly sad that it had to come to this."

Human rights activists have long criticized conditions in Japanese detention facilities, including how guards handle medical emergencies.