In Japan, people with mental illnesses have long been stigmatized, marginalized and isolated from broader society. In 2009, documentary filmmaker Kazuhiro Soda released “Mental,” a film about Masatomo Yamamoto, an elderly psychiatrist in Okayama Prefecture who respected his patients as individuals and built close relationships with them. In the process, he challenged standard psychiatric methods that leaned heavily on medication and institutionalization.

As Soda’s fly-on-the-wall camera makes clear, this was no way to get rich. Yamamoto’s hours were long and his clinic was small and rundown. Meanwhile, his wife, Yoshiko, kept domestic and professional wheels turning smoothly. Theirs was a family enterprise, with the “family” including Yamamoto’s patients.

Soda has now followed up with “Zero,” a film that revisits the now white-haired Yamamoto just as he is about to retire. Premiering at this year’s Berlin International Film Festival, “Zero” is a typical Soda documentary relying on observation and made according to his 10 self-imposed “commandments,” which include “no research” and “no meetings with subjects.”