When Japanese journalist Shiori Ito accused a prominent TV reporter of rape, becoming a rare high-profile #MeToo voice in her homeland, she was initially ignored by police, prosecutors and even much of the media.

Defying taboos, she investigated her own case, secretly recording phone calls and meetings, and compiling enough evidence to eventually win $30,000 in damages in a civil case that made headlines around the world.

That remarkable victory, which was followed last year by a toughening in Japan's antiquated rape laws, is the subject of "Black Box Diaries," a new film premiering at the Sundance festival, directed by Ito herself.