Fascist is a word that gets thrown around a bit too loosely these days.
However, when you are referring to José Antonio Kast the term couldn't be more accurate.

“If Pinochet were alive, he would have voted for me,” Kast has said.

Kast’s family has deep ties to the dictatorship. His father, Michael Kast, was a lieutenant in the Nazi army before fleeing to Chile and raising sons who shared his far-right politics. One son, Miguel Kast, was appointed by Pinochet to be minister of labor and then president of the central bank. He was one of the so-called Chicago Boys, a collection of young economists trained by Milton Friedman, set loose on Chile to launch a neoliberal experiment that saw social spending slashed and wealth funneled upward to the very rich. Christian Kast, according to journalist Javier Rebolledo’s book “A La Sombra De Los Cuervos,” was linked to peasant massacres under Pinochet, and José Antonio Kast campaigned against the the plebiscite that rewrote the Chilean Constitution and paved the way for Pinochet’s removal. “I’m not a pinochetista, but I value everything he did,” Kast has said, adding that the dictatorship “laid the foundations of modernity.”

Kast, though, is looking to roll back some of that modernity, and is running on a pledge to prohibit abortion, eliminate the Ministry of Women and Gender Equity, withdraw from the U.N. Human Rights Council, and expand prison construction.
...In 2017, José Antonio Kast proposed immediate pardons for incarcerated former members of Pinochet’s military regime.

The fact that Kast's father was literally a Nazi under Hitler should tell you something.
But what is even more surprising is that Jews in Chile don't have a problem with that.

For many Chilean Jews, the choice is clear: Most are backing the right-wing candidate, José Antonio Kast, who heads into a Dec. 19 runoff with a slight lead over rival Gabriel Boric.

As in most other Latin American Jewish communities, the majority of Chilean Jews are staunch Zionists who stand behind more conservative leaders because of their perceived support of Israel.

I find it sad that the only policy that Jews outside of the United States care about is support for Israel, and that they are willing to trade every other value for that.
Kast is also importing the the anti-science and culture-war tropes of the GOP.

Opposing him is 35-year old Gabriel Boric. You could hardly find a more different candidate.

He started in student activism in high school and in 2011, while studying law at the University of Chile, he was elected leader of its student union. That year, college students began a massive organized protest against low public funding and inequity in Chile’s education system, which Boric argued “treats our rights like consumer goods.” Marches and university occupations forced the government into negotiations that eventually yielded sweeping educational reforms.
...In 2013, Boric was elected to congress for Magallanes as an independent... Boric argues that the centrists, who have had previous stints in power, were not ambitious enough to tackle the country’s deep rooted inequality.
Boric has embraced positions, such as making currently privately-held water rights a public or common resource, which previous leftist governments in Chile have shied away from. But he cuts a relatively moderate figure, often stressing the importance of dialogue with opponents and becoming one of the most vocal supporters of a November 2019 pact between political parties to end the violence in the streets.

While Kast has pledged to defend, “resolutely and rigidly” the model, cutting taxes, regulations and public spending, Boric advocates the cancellation of student debts, an increase in the minimum wage, expansion of public health care and the introduction of new taxes on the wealthy.
Boric's biggest proposal is a plan to replace Chile’s private pension system with a state one.