Hours after winning the South Korean presidency, Lee Jae-Myung promised to “unify the people” in his inaugural speech on Wednesday.

The 61-year-old won the fast election with a 49.4% hit rate - a clear rejection of his rival Kim Moon-soo, who came from the same party, with President Yoon Suk Yeol who improvised the imp.

Yoon caused months of political chaos after he tried to impose martial law, which eventually led to his improperity.

When he was in his best job, Lee now faces a daunting task not only to unite the country, but also to its most important ally under President Trump’s unpredictable diplomatic brand, the United States.

In explicit reference to his predecessor, Democratic Lee said in his speech that he would no longer “allow democratic institutions to be threatened,” adding that he would “be the president to end separatist politics.”

A group of people speaking before the parliament - six months ago, he jumped over the outer wall and voted to decide Yoon Woo's announcement - Lee blamed the political unrest in the country on "the political faction that did not want to work for the lives of the people".

He also promised to create a "flexible, pragmatic government" and announced that it would "activate immediately" the emergency economic task force.

It was an amazing comeback for someone suspected of corruption investigated into family hatred, a man trapped in multiple political scandals - although analysts and officials say his victory was a clear capitalization of public anger.

"People believe that the martial law (the incident) on December 3 is violated by democracy," National Assembly Speaker Woo Won-Shik told BBC Korea in an exclusive interview.

“This election is not only a judgment on this, but also a reflection of the public’s requirement to properly restore the principle of democracy.”

Woo said the result was a "fair reflection of the will of the people" and a "clear expression of the people's intentions."

Park Sung -Min, president of Min Consulting, agreed, saying voters don’t have to express strong support for Lee’s agenda – instead, they are responding to what they think is a democratic breakdown”.

“Elections become tools for expressing anger… (and) are clear condemnations of the ruling party, which are accomplices or direct responsibility for martial law,” he said.

On Wednesday, dozens of Lee's supporters gathered in front of Parliament in hopes of a glimpse of the president - many said they were happy to see what he would achieve.

“I’m glad he was elected – I stayed here all night and watched the inauguration,” software engineer Leo Kil told the BBC.

"I believe he will fulfill his basic promises, such as building a fair world. I hope South Korea will be a person who makes mistakes, get the consequences of the law and the law, and execute them as promised by the people. My expectations are indeed high."

Yoo Gi-Won, another Lee supporter, said: "Yoon's presidency made me feel like this country is going to be destroyed. I see everyone around me suffer."

He added: "For a while, Korea has been cold (but now) I'm so happy."

But as the fanfare gradually disappears, Li will face a difficult reality.

First, he is still facing trial in the Supreme Court on allegations of breach of election law. The court postponed the trial until after the election was over to avoid interference, as convictions could prohibit Lee from participating in the competition.

It is unclear what would happen if Lee was convicted now, although the law says the current president cannot be prosecuted for a criminal offense, but the crime of uprising or treason.

Even bigger is the challenge of bringing together a country that is still plagued by deep anger and division.

"In the two years of the (previously) moon and the Yuan government, years of polarization have severely divided South Korea's political landscape," Mr Parker said.

“Lee may talk about national unity, but he faces a profound dilemma: how to take responsibility for many to see this as an attempted uprising without deepening the differences he is trying to heal.”

Despite the loss of PPP, former President Yoon still has a fairly strong base of voice support - and it will likely disappear soon.

His supporters, mainly young male voters and older people, often push strong right-wing narratives, many of whom viewed his declaration of martial law as a necessary condition for protecting the country.

Many also peddled conspiracy theories that Yoon's party was the victim of election fraud.

Yoon is gone, and there are questions about who might fill the vacuum for this predominantly young male base.

A name in particular appears: Lee Jun Seok, who also ran for president but exited the poll earlier on Tuesday showed he was behind.

His anti-feminist perspective made him particularly popular among many young men, reminding some women of Yoon, under which women's equality became a polarizing theme.

The number of young people in their 30s is higher than usual, and this vote was proposed in part by candidates like Lee Jun-Seok.

Those who want to hold the PPP-led government in charge, and others who want to secure Lee Jae-Myung's presidency, have resulted in a voter turnout this year at 79.4%, the highest since 1997.

In this political atmosphere, Lee took over - hope to turn public anger into hope.

How-if-he might do that, it's a question that will be closely watched.

Other reports by Woongbee Lee, Richard Kim and Haeryun Kang