The personal and the political collide in Nam Arum’s astonishingly assured debut, an astute chronicle of South Korean politics through the lens of family memories. Weaving intimate home videos with poignant archival footage, the film-maker makes tangible the invisible link between the private and the public spheres.

As a family portrait, Nam’s documentary refreshingly moves on from the usual emphasis on generational differences, focusing instead on how youthful idealism metamorphoses over the years. As part of the pro-democracy 386 generation who came of age during Chun Doo-hwan’s military dictatorship, Nam’s parents were politically active as students. Their paths following their marriage, however, took contrasting turns. Once an optimistic investigative journalist, her father chose to become a civil servant instead, and with each change of government he was arbitrarily shuffled between departments. Nam’s mother, on the other hand, devotes her time to women’s rights groups.

Though they share a loving bond, members of the Nam household have found themselves on different sides of political issues. Traumatised by the Sewol ferry disaster, Nam writes a critical letter addressing her father, who is working for the ministry of oceans and fisheries. By the time he begins his tenure in the presidential office of Park Geun-hye, his family are among the crowds of protesters calling for the president’s impeachment.

When discussing how their forms of activism have changed, Nam’s parents express an uneasiness at the thought that they had let the young people down. Nam’s documentary ends with Yoon Suk Yeol’s presidential appointment, shown here as an ominous development. As the events of the past months have shown, however, despite the worries of Nam’s parents, the democracy movement remains unstoppable among a new generation of activists. The joy of activism, as captured by Nam’s passionate film, is just as potent as ever.

• K-Family Affairs is at Bertha DocHouse, London, from 24 January.