Kim Yo Jong, believed to be 31, is already seen as her brother's de facto chief of staff and exercises significant influence in the top echelons of power.
She was recently elevated to the party's powerful politburo and earlier this year issued a scathing political statement about South Korea in her own name.
She has firm control of key party functions, setting herself up to be the main source of power behind a collective leadership, and has been credited in the past for modernising her brother's image.
In recent years, she has been seen at his side during major international summits with the US and South Korean presidents or travelling to South Korea during the 2018 Winter Olympics as an envoy in her own right.
But although Kim Yo Jong's rise would keep the regime within the family business, it remains to be seen whether she would be allowed to take over the top job as a woman.
The sudden demise of her brother could lead to political upheaval or even regime collapse.
Choe Ryong Hae
Alternatively, Kim Yo Jong could remain a figurehead alongside an elite group of senior party figures collectively steering the country through the turmoil of a leaderless country facing both the coronavirus and rising tensions with the US over its nuclear weapons programme.
At the forefront would be Vice Marshal Choe Ryong Hae, 70, who has previously also been touted as a possible successor, and who rose to be the North's nominal head of state last year when he was promoted to president of the Presidium of the Supreme People's Assembly.
It was the reward for long service in the ruling party and decades of loyalty to the ruling Kim family. He previously held the position of political head of the North's military under the young leader.
In 2019, he was one of three senior officials sanctioned by the US for human rights abuses.
Pak Pong Ju
Choe is often seen at high-level events with Pak Pong Ju, a fellow politburo member and former state premier who oversaw the North's push to introduce more free market functions to revive its economy and help it survive sanctions, and who would likely keep his influential role.
Kim Yong Chol
Kim Yong Chol, a party vice chairman and former top nuclear envoy who previously served as intelligence chief, would be an obvious choice to help lead the country's international diplomacy efforts, including the stalled denuclearisation talks with Donald Trump, the US president.
Ri Son Gwon
Kim would likely be supported by his former right-hand man Ri Son Gwon, the recently appointed foreign minister, who previously led high level talks with South Korea and who is an experienced hand in military talks after serving as a senior colonel in the national army.
