One of the sisters of a Sri Lankan woman who died in March following mistreatment at a Japanese detention facility has called on the immigration agency to accept responsibility for her sibling's death.

The family members of Ratnayake Liyanage Wishma Sandamali, 33, have been demanding that the immigration agency disclose two weeks' worth of security camera footage of her final days and clarify the cause of death, but their requests have not been granted.

"I will return (to my country) temporarily, but not because I have given up. I want the immigration authorities to accept their responsibility and prevent the same thing from happening again to other foreigners," Wishma's sister, Wayomi, 29, told reporters at Narita Airport on Thursday.