Long before she began shooting “Go for Broke: An Origin Story,” her feature film about the lauded 100th Infantry Battalion and 442nd Regimental Combat Team, producer Stacey Hayashi asked her high school pal Jake Shimabukuro to compose the music.

“I was just so honored, and of course I was scared,” said the Grammy Award-winning ukulele master in a phone interview last week. “Growing up, the Nisei veterans were my heroes. In my eyes, someone like Hans Zimmer (‘Dunkirk,’ ‘Gladiator’) should have been scoring the film.”

Shimabukuro’s “Go for Broke” song, written in 2009 for the launch of Hayashi’s graphic novel about the vets, is on his “Peace Love Ukulele” album. A simple, stirring instrumental in a minor key, it opens with a staccato, drumlike beat.

His musical influences for the film score included Hawaiian and American popular songs of that era, but his inspiration was the vets, he said. The score was recorded in a mobile studio trailer as the musicians — Shimabukuro on ukulele, baritone ukulele and guitar; Josh Nakagawa on cello; Randy Wong on double bass; Isaac Dela Cruz on violin and piano — watched the film.

“What we saw on screen influenced how we played,” said Shimabukuro, 41. “I just really wanted the music to reflect the emotion that was happening on screen.”

At a preview screening of “Go For Broke” last month, Shimabukuro held up a vintage Kamaka ukulele, carved in a pineapple shape. Given to him 15 years ago, it originally was presented to a family in Japan by a Nisei soldier who stayed with them. Shimabukuro tucked it safely away and forgot about it until Hayashi was looking for a period ukulele.

In “Go for Broke,” the instrument is strummed on a beach by Kyle Kosaki, as the young Daniel K. Inouye, on the eve of the Pearl Harbor attack.

Shimabukuro appears in the film as Saburo Maehara, an assistant in a Maui school whose teacher is arrested in the wake of the Dec. 7 attack. Having never acted, he was nervous because “the veterans and their story deserve the best,” he said.

Spoiler alert: Along with everyone else in the film, Shimabukuro delivers.

“Go for Broke: An Origin Story” screens today at 7:30 p.m. at Hawaii Theatre and 8 p.m. at Dole Cannery Stadium 18. Both screenings are sold out, but standby tickets may be available at the box offices 30 minutes before showtime.