Back in the olden days, a local archdiosce might appeal to the Vatican for a little help when it came to demonic possession of good Catholic folk in their care.

Before you could say “La plume de ma tante!” Max Von Sydow would fly in, or Russell Crowe would Vespa over dressed in black to go to war with Satan.

That’s not how they roll in the ROK. Korean exorcisms, as depicted in “The Priests” and now “Dark Nuns,” cover all the polytheistic bases — Catholocism, Buddhism and shamanism.

For the ten-years-later sequel to “Priests,” all the guys in cassocks and crucifixes are busy. So it’s up to a couple of “Dark Nuns” — one older, unordained and uncensored enough to be over this “s–t” — take up the cause of saving a boy from whatever demon in whichever of the “twelve manifestations” has moved in and turned the kid suicidal.

Director Hyeok-jae Kwon tries to match the sass, spookiness and tone of “The Priests” in a slog of a thriller that manages to be even longer and slower than the 2015 original film.

Song Hye-kyo of John Woo’s “The Crossing” movies stars as Sister Junia, stomping in with a five liter can of holy water and ready to kick ass by getting a demon to say its name.

She’s unfiltered and big on backtalk, to demons — “Coward! Taking over a child’s body!” — and to Catholic higher-ups, who as in many an exorcism movie including “The Priests” disapprove of having to “approve” this fighting-the-Devil dirty work. So they keep it at arm’s length.

Unordained or not, we’ll find you a priest to pitch in and you go, girl!

But Father Paolo (Lee Jin-wook of “Squid Game”) runs the hospital where poor Hee-joon (Moon Woo-jin) is being unsuccessfully treated.

“Possessions are not real,” Paolo argues (in Korean with English subtitles). And God, he reminds Sister Junia, “exists solely in heaven.”

He won’t be much help unless he upends his disbelief. So his young protege Sister Michaela (Jeon Yeo-been) will have to join the cursing, smoking Junia on her quest.

They appeal to the Vatican for the priests from “The Priests” to come and help. No dice. St. Francis’s Bell from that first film? Maybe. “Saint Peter’s Keys?” You know, the ones on the tarot cards?

Yes, this script, like the first film’s, spends a staggering amount of screen time on arcane Catholic myth, tortured explanations of “why” Father Kim and Father Choi can’t be bothered to help this time (the actors got more famous) and Korean polytheistic work-arounds.

Tarot, shamanism, let’s throw the works at this demon and see if we can save this boy.

Both films have decent enough effects, but neither manages the existential dread that “The Exorcist” served up and few “exorcism” films since have come close to imitating in the 50 years since.

Both “The Priests” and “Dark Nuns” go for jokes, just not enough of them. Each story is driven by a maverick Catholic character who could have been a lot more fun to hang with and root for. But neither film gets enough out of that engaging central character.

All “Dark Nuns” manages to do is provide equal opportunity for disappointment.

Rating: unrated, violence, some profanity

Cast: Song Hye-kyo, Jeon Yeo-been, Lee Jin-wook, Huh Joon-ho and Moon Woo-jin.

Credits: Directed by Hyeok-jae Kwon, scripted by Hyo-jin Oh and Kim Woo-jin. A Well Go USA release.

Running time: 1:54