This Is Us Cast Teases Season 6 Premiere — and What's to Come in 'Heartbreaking' Final Chapter

Though 2021 is coming to an end, that also means the new (and final) season of This Is Us is just around the corner.

Ahead of the sixth season of the NBC hit series, the show's creator Dan Fogelman and the cast, including Mandy Moore, Milo Ventimiglia, Chrissy Metz, Sterling K. Brown, Justin Hartley and more, spoke with PEOPLE about what audiences can expect from the premiere episode on Jan. 4. They also share new details about the final chapter for the Pearson family, which will be told over 18 episodes.

As fans will recall, season 5 ended with one couple calling off their romance while a flashforward teased a family member's second wedding.

Season 6 will kick off with the Big Three's birthday as per the show's tradition, this time with Kate, Randall and Kevin marking their 41st year in the present day. Throughout the last season, viewers will be treated to another trilogy of episodes that will each focus on a Pearson sibling as well as a Jack-centric episode about a significant death in his life.

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"The first couple of episodes are really just setting everybody up for a bit of a ride," Fogelman told PEOPLE. "It's kind of like the part of the rollercoaster where you're just ticking upwards. There are no big, gigantic or crazy things happening at the end of the first episode. This isn't a season about a build. We're kind of setting the table for an ending, and it takes a moment to build that up."

Below, the stars tease what will be explored in the final season as well as what they're excited for fans to see as many of them will direct an episode and two will serve as co-writers.

RELATED: Everything to Know About This Is Us' Final Season as You Prepare to Say Goodbye to the Pearsons

Rebecca

The first trailer of the upcoming season showed matriarch Rebecca struggling with memory loss in the present day as her Alzheimer's diagnosis progresses.

"It's really gutting. It's really sad, just so heartbreaking," Moore told PEOPLE of Rebecca's health and portraying her character, who is nearing the final stages of her life. "It's weird because I'm sort of on this parallel journey of saying goodbye to my family here and what this experience has been. Rebecca is also sort of slowly reflecting back on her life, starting to say goodbye and making her wishes known — really just savoring the time that she has left and being as present as possible."

The actress, 37, added, "It's really challenging. It's challenging not to let my grief of her situation influence what she's going through because she is handling this situation with so much grace and honesty. She's very intentional about what she wants from her life right now and how she wants to live it. The plan she makes, it's really something, but it's hard."

Moore, who will make her TV directorial debut this season, also teased that she has had "very wordy" monologues in her scripts as of late. "[Rebecca] has a lot to say to people right now," she said.

As for what she's particularly looking forward to this season? "I really am excited about exploring Rebecca and Miguel. Figuring out their courtship, how they found themselves back together and eventually getting married," she said. "I'm still excited about exploring early Jack and Rebecca days as well."

RELATED: This Is Us Creator on What's Next After Finale Wedding Twist, Kate's Second Wedding in Season 6

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Jack

Ventimiglia, who returns to the directing chair for an episode this season, is hoping fans will soak in the Jan. 4 premiere as it marks the beginning of the end.

"A lot of people really got into the show and took it as therapy, took it as a desire to communicate and change things in their own lives. So I think people who will pay attention this season, they'll embrace the same way they had in previous seasons. But also know that it's the last stop, it's the last go-around," he told PEOPLE. "We've built something that is rare in the arts, which is lasting conversation and to truly impact people, as I've heard it has people calling it to their weekly therapy sessions."

Later in the sixth season, fans will explore Jack's past like never before. "To have an episode that is purely the discovery of Jack, it's been nice to revisit," Ventimiglia, 44, said.

"It was really painful to shoot. It was about his mother's passing and dealing with that, the distance and the conversations he wished he had," the actor shared. "Jack is the guy who's always trying to be the strength of the family. What happens when that strength wears thin and it breaks, he can't always be the strength of his family. It was tough to shoot but also was very satisfying as an actor."

RELATED: Mandy Moore Feels 'Very Confident' in How This Is Us Will End: 'It's Going to Be Beautiful'

Ron Batzdorff/NBC

Kate

This year's Big Three birthday may be less of a celebration. "I think [fans] are gonna be, sort of, on edge about Rebecca's diagnosis and how that's taking place, and then how that's impacting everybody else in the family," Metz, 41, told PEOPLE, predicting how viewers could respond to the Jan. 4 premiere. "And, you know, birthdays are never what you'd like them to be."

Elsewhere in the season, audiences will see Kate's romance with her music school teacher boss and future second husband Phillip, portrayed by new cast member Chris Geere. "He's not a partner yet, because we're still, sort of, at odds in our workplace," Metz said of Kate and Phillip's dynamic at the beginning of the season. "Everyone's probably questioning like, 'What the hell is Kate thinking? This guy is a jerk.' Literally, he's 'Phillip mean jerk' in her phone. She's not interested."

Metz added, "But what's cool is we'll get to see who he really is through all of his stuff, and how that unfolds."

About the moment Kate and Phillip's relationship status changes, Geere told PEOPLE, "Fans want Kate to be happy. You can see from that flashforward [wedding] that she's happy. Life chucks curveballs all over the place, and I'm excited to read the scripts that do the transition into how they fall in love. It's finding those little moments rather than the big gestures because we're still in the present day — we have five years to fall in love."

Season 6 will also be memorable for Metz as she co-wrote the Kate-centric part of the forthcoming sibling trilogy, which costar Moore will direct. "We were totally thrown through a loop with how the show ended last season and knowing eventually what happens to Kate and Toby," Moore told PEOPLE. "It's a really important episode. It's really beautiful and heartbreaking."

RELATED: This Is Us' Chrissy Metz Drops Season 6 Hints, Shares 'Easter Egg' About Kate's Second Wedding

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Randall

First look photos from the season premiere show Randall marking his birthday separately from Kate and Kevin. "There's a bit of a separation, but it's only because we all are living very different lives right now," Metz said of the reason why the siblings could be apart from one another on their big day.

Brown, 45, was tight-lipped about the premiere but did tell PEOPLE about the upcoming Randall-centric episode. "It's a surprise. It's a road trip episode," he said, adding, "It's really, really good. [The trilogy] goes Kevin, Kate and Randall, in terms of the order of episodes. They're all really good. They're all really different and each has their own tone to it."

As for how the show will approach its series finale, Brown said he's "excited" for viewers to see how it all unfolds. "Folks have been waiting and I think we've got something good to show," he said. "I love the show. I'm biased because even when I watch the show, I watch it as a fan, not as a cast member. I feel like the show has had a really gorgeous arc and you can't create that unless you know that you have an endpoint."

Ron Batzdorff/NBC

Kevin

With Kevin turning 41, Hartley said his character is "taking a moment" and taking stock of his life as a father of twins. "He's slowing down a little bit, which is nice. I mean, he's got these kids now. He's at a totally different place," the actor, 44, told PEOPLE about the premiere episode.

Kevin is single once again on his birthday after ending his relationship with Madison (Caitlin Thompson), who is the mother of his babies and Kate's best friend. "They're gonna have to figure out how to co-parent," Thompson told PEOPLE about Kevin and Madison's future. "Whether there's something between them that blossoms or not is something you are gonna have to wait and see."

Toby

Speaking of co-parenting, Toby and Kate will be navigating how to move forward with an amicable relationship. In the present-day timeline, KaToby still exists but in the near future, their marriage will be rocked and Kate will find love again with Phillip.

On the impending split, Chris Sullivan told PEOPLE, "Fans don't want to see characters that they care about hurting. Unfortunately, that type of pain is a part of life. I think an interesting thing that Dan and the writing staff have done is give us these handbooks for relationships. If they're going to show us every aspect of relationships then somebody's got to break up at some point — and it ain't gonna be Randall and Beth."

The actor, who will also be making his TV directorial debut this season, added: "Co-parenting is not an uncommon thing. There are ways to do it that are healthy and beneficial for all the people involved, and there are destructive ways to do it. Toby and Kate are going to hopefully be a good example of how to navigate a situation like that."

Ron Batzdorff/NBC

Beth

Susan Kelechi Watson was able to co-write an episode for the final chapter, and it's an important script for the actress as it will further dive into her character Beth. "I got to kind of write Beth's final opus so it's really beautiful," Watson told PEOPLE about the episode titled "Our Little Island Girl: Part Two."

While fans will have to wait until the sixth season's sixth episode to watch the Beth-centric storyline, Watson dropped hints about the premiere. "The emotion of it in terms of dealing with what's now going on with Rebecca and then the Big Three are all equally dealing with their own stuff as we left off with last season," she teased. "For some reason, they always seem to reckon with that stuff on their birthday. They never enjoy their birthday. Just enjoy the day!"

Miguel

"This season, we're gonna open up a little bit more of Miguel," Jon Huertas told PEOPLE. "We're gonna open up a lot more of Miguel and Rebecca's story, which has been amazing to film and discover that Mandy and I have great chemistry."

Fans of Jack may have been hesitant about coming around to Miguel's romance with Rebecca but Huertas thinks the last season will sway some viewers to love his character. "When you start playing with their romance a little bit more, it's like, 'Oh, this is cool.' We've had so much fun doing it, I think that's going to translate through the screen. When the actors are having fun and like the story they're telling, the audience feels that. I think that's going to help anybody who's apprehensive about Miguel and, hopefully say, 'I'm rooting for these two.' "

Laughing about how fans now have Phillip as a new character to be apprehensive about, Huertas joked: "So glad he's here because they hate him." (Geere jokingly told PEOPLE, "There's a real kind of curse on any guy that comes into contact with a female Pearson.")

As for the premiere episode and what to expect, Huertas teased: "In the first couple of episodes, there are some things that people are going to want some answers as to what we're setting up. Some things are different, some living arrangements are different."

Season 6 of This Is Us premieres Jan. 4 on NBC.