What if the couple in Jason Robert Brown’s musical “The Last Five Years” were serial killers instead of a writer and an actress.

That was part of the inspiration for “Serial Monogamy,” the latest musical by Robert Dennick Joki and Josh Taylor, which Rust Belt Theater Company will stage for a three-weekend run starting Friday at the Calvin Center.

“I love that musical and sang a lot of the music in college,” Joki said. “But these two people are completely full of themselves. In my mind, it wasn’t that big of a stretch to think these narcissists would probably be serial killers if they weren’t artists.”

The first incarnation of “Serial Monogamy” was a 10-, 15-minute comedy written a decade ago as part of an evening of one-act plays. That sketch also was worked into Rust Belt’s poplar musical revue “Dating Sucks” one year.

“I always thought it was a lot of fun, and the audience reacted really well to it,” he said. “The option of turning it into a longer show always was on the back burner.”

Joki often presents ideas to the actors he regularly works with when trying to assemble a season, and “Serial Monogamy” was one of the proposals that got the most support.

Even though the new version is much longer, Joki quickly realized he had to abandon much of the original.

“When you had to introduce the characters and wrap everything up in 15 minutes, jokes and gimmicks that work in a very short play don’t work over the course of two hours,” he said.

He compared the transformation to being similar to what happened with “Buffy the Vampire Slayer,” which started as a quirky, campy standalone film and evolved into a more serious, expansive tale that could play on television for seven seasons.

“It’s still a comedy, but much darker than what I originally wrote,” he said. “There’s a lot more room for character development.”

The two main characters in “Serial Monogamy” both have a passion for murder but take different approaches to the crime.

“Elizabeth is calculating; her murders are well-planned,” Joki said. “James is more of a spur-of-the-moment, just-see-someone-and-kill-them kind of person. Elizabeth is always reading up on the most prolific murderers of all time, and many of musical numbers are how she would imagine these people from history going about their business.”

The cast features Austin Brown, Lynn Sabeh, Martin Daniels, Rachel Clifford, Leah Ifft, Geri Dewitt, Kage Coven, Jack Rusk, Jude Mikulich, Brooke Nobbs, Mary Boldish Janes, Josh Yohman, Erik Glasgow and Celena Coven.

“I haven’t been as excited about anything I’ve written in a long time,” Joki said. “I’m really excited to get this in front of an audience.”