Two cousins, once close as youngsters, are given a trip to trace their roots back in Poland. For both, because they are opposites in every way, it becomes “A Real Pain.”

Jesse Eisenberg, who wrote, directed and stars as married and uptight David Kaplan, has generated Best Original Screenplay Oscar buzz with a movie that is somehow truly funny and incredibly bleak.

“Succession” Emmy and Golden Globe winner Kieran Culkin plays go-with-the-flow, free spirited but lonely and lost cousin Benji Kaplan. He too is generating Best Supporting Actor Oscar buzz.

Culkin, 42, recalled, in a virtual press conference, that he’d signed on prior to filming the last season of “Succession.”

“I immediately clicked with the character and felt, ‘I know how to do this.’ For me I can picture them as kids and know how they got that way. It was an easy yes.”

But not an easy movie to make for this father of two who is, famously, from a showbiz family, the fourth of seven children.

“We finished ‘Succession’ two months later than we thought. Then they pulled up the start of ‘Pain’ by a month — and I wanted to be home with the wife and kids. But I was to be away for 25 days.

“So then I tried to pull out — and there was no way because of the nature of the shoot. My kids are one and three — I couldn’t bring them. It would be a nightmare for me personally!

“So why am I doing this? Because, creatively, this was the one I wanted to do. So I did it — and I’m really glad I did.”

Did his costar surprise him as director?

“I don’t know if surprised is the word. Going in he’s wearing three hats. The script is great and I’ve seen him as an actor.  I felt it was going to work out well.

“But what’s he going to be like talking to actors? We’re about the same age and have done this the same amount of time. I don’t know if I could direct but I’d like to do it the way he did it. He’s very inclusive. It felt like we were all making his film.

“I’ve never been,” he noted, “in a scene with another actor directing.”

Easily the most disturbing if memorable moments in “Pain” come when they visit the actual Majdanek concentration camp where a million-plus Jews were murdered.

“When we went, the drive from the hotel to the concentration camp was literally five minutes. We shot it the way he wrote it. We didn’t go into the room until ‘Action’ was said. One take, maybe two. Like an actual tour group, we were all taking it in.”

“A Real Pain” opens Nov. 15