Sequels can seem like setups for failure, especially when the movie you’re writing a sequel to was the highest-grossing animated film of all time and the 16th highest-grossing film in any genre. (And, you won the Oscar for Best Original Song.) Yet Frozen songwriters and co-creators Kristen Anderson-Lopez and Bobby Lopez set out to devise a Frozen 2, with collaborators Jennifer Lee and Chris Buck, that would be The Empire Strikes Back of sequels—according to Lopez.

“With a musical sequel, our concern was even greater [about singability] because it’s hard to make the same characters that you know sing again,” Lopez confesses. “You have to really have something else to sing about.” The box office indicates they found their sweet spot, since Frozen 2 topped its predecessor as the highest-grossing animated film in history.

But more than a financial hit, the triumph of Frozen 2 emanates from the originality, maturity, and strength of its story and the invigorated sound of its songs that build on the foundation of the first film—without recycling plot points or themes. The team completed intense character investigation and immersive research to arrive at the core of Frozen 2. Director and writer Jennifer Lee took personality tests as Anna and Elsa. “She was taking the Myers-Brigg,” Anderson-Lopez reveals. “She did a whole day with a psychologist as Anna and a whole day with a psychologist as Elsa so that she identified the places where there were still wounds.”

What the team discovered is that Anna had questions about why her family hadn’t told her the truth about Elsa; and Elsa had questions, now that her powers had been accepted by the community, about why she had them. As the team explored these questions, they also physically explored the terrain of Nordic countries like Iceland, Norway, and Scotland’s Orkney Isles and the history of the peoples there.

But what’s most fascinating is that the Lopezes worked simultaneously on the stage adaptation of Frozen for Broadway and the all-new Frozen 2. Much of what they learned via Frozen Broadway informed the sequel, and now, the sequel has inspired revisions in the stage musical.

Ahead of Frozen 2's home video release February 25, Playbill sat down with the Lopezes to dig into writing a new score for Frozen 2, making changes to Frozen onstage, and whether or not we might see Frozen 2 on Broadway.

READ: Kristen and Bobby Lopez Reveal New Movie Musical

On finding the sound of Frozen 2:
Film composer Christophe Beck had introduced a Scandinavian sound in his finished score for the first Frozen film, which inspired the Lopezes to dig deeper into that cultural richness. “We had done a lot of research for the first film on the indigenous people, the Sámi people, around Kristoff. But when we realized there was a lot more to tell there, about political landscapes and the fight over resources and things like that, we took a much deeper dive into the indigenous peoples of the North,” says Anderson-Lopez. “There was something about that reparations that we were all in discussion about—the way that there’s an entire culture that had to go underground, or go so far North that nobody ever wanted to follow them.”

In Elsa’s “Into the Unknown” (nominated for the Oscar for Best Original Song), the Lopezes honored the Norwegian tradition of kulning, or herding calls used to call livestock down from their daily pastures. The wistful soprano of Norwegian singer Aurora, in contrast to Idina Menzel’s gritty belt, uses the melody of the “Dies Irae” with a kulning bent. Anderson-Lopez says, “It’s the same idea of a shepherdess of some sort calling Elsa home.”

On the animation’s impact on the score:

“Before we had a single song, we were looking at visual development, a mural of that shot of the four main characters—five, if you include Sven—looking over the forest,” says Anderson-Lopez. “That was so expansive and almost like Hudson River School of Painting. Out of that experience bubbles up ‘Into the Unknown’ because you’re looking at it and that’s what that picture is telling you.” As the Lopezes composed, animator Norman Moses Joseph illustrated Elsa seeing things that were going to happen in the forest. “Looking at that and seeing that her powers were coming out actually inspired us to go much bigger with the ending than it was,” Lopez adds, “[The animators] found that idea because there had been a scene called ‘Elsa’s Dream’ where her dreams played out in snow above her head, and Anna saw all those things and all of those creatures. But then it seemed like that scene should really be incorporated into ‘Into the Unknown’ and make her powers come alive that way. That was a moment of inspiration, of taking one visual and marrying it with a song.”

How writing Frozen for Broadway and Frozen 2 simultaneously fed both artistic endeavors:

Frozen 2 rewinds to Anna and Elsa’s childhood and the relationship with their mother—an idea that came to the Lopezes from adapting the first movie for Broadway. “The mother really didn’t have any lines at all in the first movie; she was a blank canvas that we could fill with something exciting, and a secret,” Lopez says. “There was a day when we were writing both the Broadway show and Frozen 2 and we wrote that lullaby [‘All Is Found’]. It was the same character, on the same night [in the story], but in two different media.”

“All Is Found” had been embedded in their original opening number “Anna and Elsa” in the out-of-town tryout, but was cut in tech for Broadway. “In that moment, you went inside the mom’s head about worrying about Elsa, about knowing there’s something different about Elsa and ‘what I wouldn’t do to help make her life easier,’” says Kristen. “And we love that character,” Lopez interjects, “and the lullaby was an attempt to really strike out a new tone for Frozen 2. We listened to a lot of Scandinavian folk songs and lullabies and they’re all in this minor key and they’re all very mysterious. It’s haunting and it feels epic in a way. And the lyrics point the way to the adventure and the secrets that they’re going to discover.”

More than a song and tonal inspiration, Broadway’s Frozen helped clarify Kristoff as the duo considered his trajectory in Frozen 2. “We did get to find a lot more of Kristoff’s humor while working on the Broadway version—where the sweet spot for Kristoff is as this sort of modern Marlboro Man,” says Anderson-Lopez.

The team also discovered a useful tool in the writing process. “We had to really whip the score up very fast for Frozen Broadway,” Lopez recalls. “We would sometimes say to Jen, ‘For the coronation, in your mind, how is she feeling?’ And Jen would write a page of inner monologue, a free-write as Elsa.” Adopting that process for Frozen 2, the Lopezes wrote Anna’s ‘The Next Right Thing’ based on a monologue crafted by Lee and Kristen Bell, who voices Anna.

On making changes to Broadway three years in:

Frozen launched its first national tour November 10, 2019. Audiences who experienced the Broadway show first may have noticed a few changes—which were then incorporated to the Broadway production February 18. Anna’s Act 2 ballad “True Love” has been cut. But rather than shorten the musical, that allowed the Lopezes to insert a song earlier in Act 2 that they had always intended to write.

“We had always planned on writing a song called ‘I Can’t Lose You,’” says Anderson-Lopez. The songwriting duo wanted the duet to come when Anna finds her sister locked away in her ice castle, where the “First Time in Forever” reprise previously landed. The moment demands more.

“Anna is saying, ‘I can’t lose you again like I lost you in my childhood,’ and Elsa is saying, ‘I can’t lose you; I can’t let you die following my quest,’” explains Anderson-Lopez. For the first time, the Lopezes had the breathing room to write that song.

“[Disney Theatrical’s Tom Schumacher] found us at the right moment when we were wrapping up our writing work on Frozen 2 and we were starting to feel a little bit scared and sad that it would be the last time we’d ever get to write for Anna and Elsa, and he gave us this assignment and we were like, ‘Oh thank God, yes! We want to keep doing this,’” says Lopez. Anderson-Lopez adds, “We wanted to take the sister relationship that much deeper.”

WATCH: Frozen's Ciara Renée and McKenzie Kurtz Perform ’I Can't Lose You’

On the possibility of Frozen 2 coming to Broadway:
Though there are no plans announced for a musical stage adaptation of the sequel, the pair won’t rule out the possibility. “I’ve always thought it could be fun to do it like Harry Potter. To do a night one and night two,” says Anderson-Lopez. “But in a decade.”

“We did a little concert on the Disney cruise we took,” Lopez adds. “Some of the performers who are in the Frozen show on the cruise ship sang, and [the songs] did work well on stage.” It could be the next right thing.

Missing “True Love”? Watch how the Lopezes wrote the now cut song for Broadway’s Frozen: