In the world of stage and entertainment, it’s not uncommon to have one person play two roles. Less common is to have two characters play one — unless it’s a “Bewitching” situation where Dick Sargent replaced Dick York. It’s also not unheard of to have men play a female role — just witness the film “Jumanji: In the Jungle.”

But it would be safe to say that none of those is quite as innovative as “As One,” a chamber opera presented by Hawaii Opera Theatre starting next week. The opera has only character, a transgender person named Hannah, who over the course of the opera transitions from male to female. Hannah is portrayed by the husband-wife duo of baritone Kelly Markgraf and mezzo-soprano Sasha Cooke, who as “Hannah before” and “Hannah after” simultaneously experience life through the prism of both genders.

In its four-year history “As One” has become a favorite among small opera ensembles, with more than a dozen productions already staged and several more planned for this year. The New York Classical Review called it “everything we hoped for in contemporary opera: topical, poignant, daring and beautifully written.”

For Cooke, a Grammy-winning operatic singer, and Markgraf, known for his versatility in classical, pop and jazz roles, the appearance here will mark a homecoming of sorts; Cooke is a direct descendant of Amos Cooke, the missionary and businessman who laid the groundwork for Castle & Cooke, one of Hawaii’s “Big Five” corporations. The pair got married here and visit as often as possible.

Markgraf and Cooke gave the world premiere of “As One” in 2014, but HOT’s production will be only their second time performing it together since then, as both are in heavy demand by opera companies around the world.

“I haven’t been free for any of the ones I was requested to do, but Hawaii was awesome because they really worked around our schedule to make it work,” said Cooke, speaking from her home in Texas a few days after performances in Germany.

“As One” had its genesis in 2012, when New Jersey, along with other states, was wrestling with the issue of same-sex marriage. Composer Laura Kaminsky read a newspaper story about a husband, who, with his wife’s support, was planning to undergo gender reassignment. New Jersey did not recognize same-sex marriages at the time, so once the man transitioned, their union would have been derecognized and all the benefits derived from marriage — Social Security, health insurance, retirement — would be in jeopardy.

“They were in love as people, not as body parts, and if the law did not pass in New Jersey, they would no longer be married and they’d lose all those benefits,” she said. “As I read the article, I was thinking, ‘This is operatic. … What is it to be a fully realized human being, in the context of the people in your orbit, and then what are you willing to give up in order to gain yourself?’”

It a took a number of random events to bring “As One” to fruition in its final form. Kaminsky, a respected composer of contemporary music, had never created an opera before and until then had never been interested in doing so. But during a visit to Russia she obtained some rarely performed Shostakovich scores, and seeking someone to perform them, connected with Cooke, whose parents are Russian-language professors in Texas, and Markgraf.

“I fell in love with them,” Kaminsky said. “They’re extraordinary artists, but it’s because they’re extraordinary human beings. They’re deeply empathic, spiritual and empathetic and intellectual all at once. … I wanted them to be in my opera; in fact, I wanted them to ‘be’ my opera. I wanted them to be the one character.”

Kaminsky came across the story of filmmaker Kimberly Reed, a transgender person whose story of transition from male to female and her interaction with her rural hometown was told in the film “Prodigal Sons.” Kaminsky teamed up Reed with Mark Campbell, a respected opera librettist, to come up with a story, tossing a few ideas around initially but not coming up with anything.

“I started talking to Kim (Reed), saying, ‘Why don’t you tell me about some of your experiences as a transgender person?’” Campbell said. “She talked about having a bicycle route, the way all boys did when people looked at newspapers, and one day she decided to do it in a blouse.”

That incident would eventually become the opening scene of “As One.”

Much of the opera reflects Reed’s experience, but it is not biographical, Campbell said. Some parts are drawn from other known incidents, such as assaults on transgender people.

For Campbell, “As One,” while reflecting the particulars of a transgender person, has a universality that will make the story relevant to people no matter their interest or knowledge of the issues.

“This is about a person’s happiness,” said Campbell, who as a gay man identified with some of the identity issues raised in the opera.

“If you know a transgender person, you will realize that there is nothing different about them, that they are just seeking happiness. They were not born with a gender they feel they are. Why would you deny someone’s happiness? If you reduce it to that, most people cannot fight it.”

“As One” traces Hannah’s journey in 15 vignettelike songs, many of them sung by both singers as they reflect on incidents from a male or female perspective. For example, in a song about a grade school handwriting class, “Cursive,” Markgraf as “Hannah before” stresses out over writing in a restrictive, masculine style; Cooke as “Hannah after” worries about writing “like my cousin Annie” with “generous loops” and “graceful swirls.”

For Cooke and Markgraf, “As One” was a revelation into gender behavior, especially in children.

“I didn’t really fully understand what it meant to be transgender and how early kids have the feeling that they’re in the wrong body. All of that really blew my mind,” said Cooke, who won a Grammy for her role in the Metropolitan Opera’s recording of John Adams’ “Doctor Atomic.”

“As One” required them to inhabit each other’s persona fully. One Hannah might be singing, for example, while the other is acting out the confused emotions underlying the song.

“Sometimes the person who’s not singing acts more,” Cooke said.

Being married proved to be advantageous in working that out.

“We’re so comfortable with each other,” she said. “We share one mind sometimes.”

Musically, “As One” is written in Kaminsky’s jazzy, contemporary style, played by a string quartet. It was a challenge for the singers but has proved accessible for listeners.

One of the tunes. “To Know,” has come to be considered the high point of the work. Sung by both performers, it expresses the excitement of discovering transgenderism for the first time.

Markgraf considers another song, “Perfect Boy,” in the first act, to be pivotal.

“It really goes to the heart of what forces are at play,” he said. “Hannah before is really truly trying to suppress and push down all of these things because of family influence and societal influence, because of all the inculcation that happens as we’re being raised. … It’s this repetitive ‘Push down, push down. No, I will not be seen this way, I will not feel this way.’”

Markgraf, who has performed as Hannah before in two other productions, said the work has provoked heartfelt, emotional responses, not only from transgender people, but people who knew little of the subject before experiencing the show.

Cooke added that people should not worry about feeling squeamish about the subject matter.

“I think a lot of people that come to this show expect or maybe wonder if they’ll be uncomfortable,” she said. “It’s quite the opposite. Transgender is merely an avenue to discuss accepting yourself. Any person, everybody can relate to that journey of, ‘What do I really want out of this life. Who am I?’”