Last week a new movie called “Railways” opened in Tokyo. It’s about a driver on a small rural electric train line who retires after 40 years and is sort of a sequel to a film with the exact same title released in 2010. That movie centered on a Tokyo executive who loses his job and decides to pursue his boyhood dream of becoming a train driver. Both films appeal to male boomers, but the nostalgic interest central to the newer movie’s promotion has to do less with its subject than with its 59-year-old star.

Tomokazu Miura has been an actor since he was 18, and a surprisingly successful one considering his narrow range and lack of on-screen charisma. His show-business longevity is based on one ancillary attribute: He is married to Momoe Yamaguchi, the most popular idol singer of the 1970s, who retired at the age of 21 in 1980 to marry Miura. Since then she has never made a comeback, nor has she appeared in public in any capacity except as the object of paparazzi. These days her only connection to the larger world is her husband, who over the years has never talked about her or their marriage in any meaningful way, even though he seems to understand that his career was more or less based on the fact that he was Mr. Momoe Yamaguchi.

In the past month, however, while doing promotion for “Railways,” Miura has agreed to talk about his private life. In fact, the movie’s release coincides with the publication of a memoir, “Aisho,” which Miura wrote at the urging of the publisher that backed the film. The actor has said that initially he didn’t want to write a book about himself, but filming ended around the time of the earthquake last March and he decided he could help victims by donating all proceeds from sales of the book to relief efforts. It’s been one of Amazon Japan’s Top 20 best-sellers since it was published in November.

Aisho means “compatibility,” the word Miura uses to explain the success of his marriage, which he agreed to discuss in at least two long interviews, one on NHK’s information show “Asaichi” and the other in the magazine Shukan Bunshun. Yamaguchi fans hoping to hear of her return to the limelight or at least some juicy anecdotes were probably disappointed. Based on what he said, Miura’s past reticence regarding his conjugal life would appear to have less to do with protecting his privacy than with the fact that there isn’t anything to talk about.

The conversations made clear that Miura’s career is mostly a series of lucky accidents that happened to a nice guy with little ambition and even less talent. In high school in the late 60s, he wanted to be a musician and was a member of the group that eventually became RC Succession, the influential folk-rock ensemble lead by the late Kiyoshiro Imawano. Miura’s tentative involvement with the band was exemplified by the instrument he played: bongos. When they were taken on by a production company he was dropped, but the same company, impressed with his looks, took him on as an actor.

He didn’t become famous until he was hired for a 1974 TV commercial for the confectionery Glico. He was paired with 14-year-old idol singer Yamaguchi, and a year later, when Yamaguchi was cast in her first movie as the title character in the film adaptation of Nobel prize winer Yasunari Kawabata’s “Izu Dancer,” the producer, looking for a suitable costar, chose Miura based on the Glico ad. This casting decision sealed their fate. Not only did the CMs continue, but Miura and Yamaguchi costarred in 12 more movies over the next seven years, many of them based on prestigious literary works.

If Miura’s success in the ’70s was tied to serendipity, Yamaguchi’s was mostly inadvertent. Presented by her handlers as the antithesis of the virginal idol stereotype, Momoe projected a darker, damaged image, her songs implying a girl who possessed if not actual sexual experience then at least knowledge of what men were capable of. Raised in a broken home, Yamaguchi reportedly resented playing this role, and once she married Miura she completely turned her back on it.

But Miura, now responsible for a wife and, soon, a family, had to move forward. He admitted that he was surprised when Yamaguchi told him on the eve of their wedding that she planned to quit. He knew his career was tied to her, and for a number of years afterward he was “depressed” since it was difficult to get work. The turning point came with the film “Typhoon Club” in 1985, in which he played against majime (earnest) type as a dissolute schoolteacher.

But as the years progressed Yamaguchi’s mystique only increased and her old records continued to sell well. Consequently, Miura’s identity as the only public person connected to her remained his primary sales point. As he told Bunshun, after many years of refusing to talk about Yamaguchi he discovered that reporters had stopped asking, which in turn made him wonder if they were just being polite. Apparently, even he didn’t understand why anyone would want to talk to him otherwise.

So why start talking now? Miura turns 60 next month and for whatever reason has become secure as a fixture in the public imagination. His children are grown and out of the house (one son is an actor and had a part in the first “Railways” feature), so what’s the harm in giving people what they want, especially when there isn’t much to give?

Miura claims that he and his wife never fight or talk about the old days. If anything, they sound like a typical middle-class, middle-aged couple; maybe even more boring than a typical middle-class, middle-aged couple. This sort of normality apparently suits Yamaguchi, who was never comfortable as a celebrity and seems to have always understood her limits as a performer, just as Miura seems to understand his. What the public understands is a completely different matter.