Each year in Japan, so the on-screen text of Johatsu tells us, about 80,000 people go missing in Japan. Most of them either return home or are found. A small proportion are simply never heard from again. Among those permanently vanished people are those that, for a variety of reasons, choose to abandon their homes and lives for an anonymous existence somewhere else in the country. Mori Arata and Andreas Hartmann’s documentary approaches the johatsu phenomenon – the word literally means “evaporation” – through the experience of the disappeared themselves, the family they often leave behind, and the people who make a living out of helping these runaways establish new lives someplace else.

Given the subject matter, it is not a surprise that for at least some of the people interviewed their participation came on the condition that the film never be screened in Japan. That seems a likely case for Kanda, a man in late middle-age who fled gambling debts owed to organised criminals. He lives a listless, nameless existence now, working anonymously in construction while continuing to spend much of his money gambling. While his disappearance makes a clear sort of sense, for other featured people it seems less understandable. One subject abandoned his wife and children after driving the family business to bankruptcy. Another hides from what they feel are controlling parents.

Perhaps the most painful to watch of those featured in the documentary is Goto, a doting mother whose son chose to disappear from her life. The police cannot help, as her son is not technically missing. Privacy laws ensure she cannot legally track him down herself. Wishing only to communicate with him, she has resorted to hiring a private investigator to seek him out on her behalf. It is a hard segment of the film to watch, as it seems soaks in not only emotional hurt but a genuine lack of understanding: Goto simply cannot fathom what her son has done and why.

Time is also spent with Saita, a woman who runs her own agency as a ‘night mover’: helping the disappeared to make their exit from their old life, ensuring they do not leave a trail behind, and coaching them on how to establish their new, anonymous existence. It seems an unusual career to have, and it is fascinating to learn the cost that such a profession has taken on Saita’s own domestic life.

Interviews are interspersed with unsettling imagery of Japan’s vast, similarly anonymous cities – all cold, endless architecture into which people can so readily vanish. A melancholy pall hangs over the entire affair like a thick, slightly worrying fog. To my Australian eyes Japan can often seem a strange and unfamiliar country. Johatsu exposes and explores some of that unfamiliarity, but I do not think anybody can fully explain it. This a documentary that both illuminates human behaviour but also showcases what seems ultimately inexplicable.