Kim Jong Un has ruled North Korea for 15 years without once publicly naming his mother – a silence unusual even by Pyongyang’s secretive standards, where political mythology is part and parcel of the regime’s self justification for existing.

Omission in this manner is thus rarely accidental. It is wholly deliberate. In recent weeks the BBC has reported that legitimacy in North Korea is tightly bound to a hereditary narrative linked to the so-called Mount Paektu bloodline claimed by both Kim’s father and grandfather, Kim Jong-il and Kim Il-sung.

Any deviation from this official family story is seen as a political threat rather than a biographical detail – one North Koreans would be executed for at the drop of a hat should the ruling Worker’s Party get wind of such claims.

At the centre of the maternal question for Kim Jong Un is Ko Yong Hui, or as she was known in Japan, Takada Hime. Widely believed to have been born in Osaka in the early 1950s to parents from Jeju Island off South Korea, a background as a Zainichi Korean in Japan – a term formed during Japan’s colonial rule of the Korean peninsula from 1910 to 1945 – came about as many Zainichi remained in Japan after the war.

In doing so they often faced discrimination in employment and education as well as in the ability to secure housing. Over time, this pressure led many to conceal their Korean identity and adopt Japanese names. It is a reality still seen today in Japan where millions of those with Zainichi Korean lineage limit any public expression of heritage in order to avoid prejudice and social shame.

The experience of Zainichi Koreans therefore is central to understanding Ko’s early life. Identity was oftentimes hidden outside the home. Even within families, the decision to reveal or conceal links to the Korean peninsula and Korean origin could shape career prospects and social mobility. This continues in the 21st Century regardless of official Japanese claims otherwise.

Against this backdrop, Ko’s later move to North Korea served as a geographic displacement shifting her from one highly stratified system of hidden identity to another.

Ko’s family is believed to have moved to the North when she was around 10 years old or potentially in her early teens as part of a broader state-backed ‘repatriation’ programme of sorts. This took place between the late 1950s and 1984.

Ethnic Koreans – many the Zainichi Koreans forced to hid their identity in Japanese society – were promised free healthcare in addition to quality education and economic opportunities they would have little chance of enjoying across the Sea of Japan. Over 90,000 people are believed to have taken part but early arrivals back on the peninsula were often greeted with curiosity and even envy, as they brought consumer goods and capital from Japan.

These perceptions soon hardened though and returnees were increasingly labelled “jjaepo”, a derogatory term implying ideological contamination from a capitalist society.

Within North Korea’s rigid social classification system, known as songbun, they were frequently placed in lower tiers, just as they were in Japan, in a system that functioned as a form of inherited stratification, shaping access to universities, political positions and even food distribution when times became hard.

The BBC describes songbun as one of the most entrenched mechanisms of social control in North Korea, claiming that it determined life chances across generations. This is an understatement. Songbun is akin to the now largely outdated Indian caste system – but one from which there is no escape.

Within this hierarchy, families of returnees often occupied a so-called ‘wavering’ class, those neither fully trusted nor entirely excluded. People in this group remained under surveillance from within while facing structural ceilings on advancement.

As such, for someone like Ko, this background carried long-term implications and struggles, even after she entered elite artistic circles.

Still likely in her teens she joined the Mansudae Art Troupe, an specialist performance unit closely linked to the North Korean leadership and it was through this route that she reportedly came to the attention of Kim Jong Il – Kim Jong Un’s father.

At the time, Kim was already being groomed for succession and had an arranged marriage alongside a number of other relationships most reliable sources on the Kim regime report.

Despite this, at some point Ko is believed to have become one of his favourite sexual companions even if her relationship with Kim Jong Il remained unofficial.

But under North Korea’s heavily codified social order, children born outside formal marriage then, and now, carry significant stigma, particularly within high class families. Because of this, Ko and her children are believed to have lived outside Pyongyang, in relative seclusion.

To date, Ko has never appeared in official propaganda by name – an example of the sensitivity over her background as a Japan-born Zainichi Korean – even if a rare documentary later shown internally to senior officials in Pyongyang briefly depicted her alongside Kim Jong Il according to the British broadcaster.

That film was quickly withdrawn after circulating beyond authorised circles in a demonstration of just how tightly controlled personal narratives are within the North Korean autocracy.

Ko herself died of breast cancer in 2004 in Paris. At the time her passing was ignored by state media. What little is known is reconstructed largely through defectors to the South, Japanese investigative journalists and intelligence agencies in Seoul.

With the politics of legitimacy so crucial to the Kims however, Ko’s children were not initially seen as the only contenders for the North Korean throne. Kim Jong Il’s eldest son, Kim Jong Nam, was once considered a possible successor but fell from favour soon after being caught at Tokyo Disneyland in Japan and spending extended periods abroad. Living something of a playboy lifestyle, he was later assassinated by North Korean agents in Malaysia in 2017.

Another son, Kim Jong Chul, was deemed unsuitable thanks to a questionable temperament and health issues. There has been talk of drug abuse. In time this led to Ko’s son, Kim Jong Un, emerging as the preferred heir, and when Kim Jong Il died in 2011 after an extended illness, Kim Jong Un assumed power at the age of 27.

And as the BBC correctly noted, unlike his father and grandfather, Kim Jong Un’s birthday is not officially celebrated as a national holiday. This is more than likely because of, or at least linked to his maternal lineage and the Japan connection given difficulties that would arise once public attention was drawn to to his full family background. In North Korea, as in many oppressive states, silence on an issue is protection.

Compounding the whole issue is North Korea’s historical relationship with Japan which adds another layer of sensitivity to Ko’s origins. Between the late 1970s and early 1980s, North Korean agents abducted hundreds of Japanese citizens from Japanese territory and elsewhere in the region – perhaps most famously schoolgirl Megumi Yokota. The issue became a major diplomatic crisis in the late 1990s and early 2000s, until in 2002, then Japanese prime minister Junichiro Koizumi made a landmark visit to Pyongyang to address the matter directly with Kim Jong Il.

That visit led to the return of five abductees to Japan, while many others remain unaccounted for and as North Korea has never fully addressed or recognised the abductions, the issue continues to shape mistrust between Tokyo and Pyongyang.

To this end, with such historical grievances and remaining political sore points in both countries influencing public sentiment and diplomatic engagement even decades later, any admission that the mother of North Korea’s Supreme Leader was born in Japan would be a hammer blow to the legitimacy of Kim as the rightful head of state.

It would instantly add weight to anti-Kim elements in the military or political elite and general populace of North Korea if these even exist.

So for now, Ko Yong Hui’s Japanese background, more than 20 years after her death, the rigidity of North Korea’s songbun system, and the politics of dynastic succession in the most oppressive state on the planet mean that the continued silence around Kim Jong Un’s mother is not merely biographical, it is political architecture set in stone.