It has been 50 years since the publication of the first manga by Go Nagai, the mastermind behind classic properties such as “Devilman,” “Cutie Honey” and “Mazinger Z.” To mark the occasion, a number of Go Nagai anime adaptations are out this year, including the film “Mazinger Z/Infinity” (Jan. 13).

“Infinity,” a sequel to the original 1970s “Mazinger Z” series, centers around Koji Kabuto, pilot of the titular super robot, who defeated the dastardly Dr. Hell at the tender age of 16. In the new film, Koji is 10 years older — and in possession of a brand-new voice. Showtaro Morikubo takes over the role from Hiroya Ishimaru, who starred as Koji in both the original series and many of its spinoffs.

“Basically, I was told to do it the same way Ishimaru did,” Morikubo tells The Japan Times ahead of the film’s premiere. But when he asked the veteran voice actor (who himself has a cameo in the film) for advice on the role, Morikubo says, “I think he was half-joking, but he told me, ‘It was too long ago! I don’t remember! Just make it your own.'”

After all, the Koji of “Infinity” is no longer a hot-headed teenager. Now in his late 20s, he has retired as a robot pilot and become a prominent researcher. But when Dr. Hell reappears, Koji finds himself drawn back into battle — and into an internal struggle about what it means to be a grown-up.

“He’s right on that borderline between child and adult … there are scenes in which he thinks, ‘Wait a minute, I thought I was more mature than this!'” Morikubo says.

Indeed, for a sequel to a series in which physics are practically nonexistent, Mazinger Z’s most powerful attack is called “Breast Fire,” and the villains’ names are as subtle as, well, Dr. Hell, “Infinity” is filled with some surprisingly deep themes. In-between robot battles, the film takes time to contemplate adulthood, war, politics, and even good and evil — and who gets to decide which is which.

“It’s a timeless theme,” Morikubo says. “Dr. Hell may say some horrific things … but what he’s doing is correct from his own point of view.”

For Morikubo, like many Japanese people of a certain age, Go Nagai’s creations were a big part of childhood (he distinctly remembers proposing his parents name his younger sister after a character from “Mazinger” sequel “UFO Robot Grendizer”). Asked why Nagai’s works continue to be popular half a century after their debut, Morikubo speculates the same deep themes that appear in “Infinity” may have been there all along.

“When you’re a kid, the robots are the attraction, but if you revisit Nagai’s works as an adult, they take on a whole different meaning.”

“Plus,” he adds, “it’s just really fun.”

In line with COVID-19 guidelines, the government is strongly requesting that residents and visitors exercise caution if they choose to visit bars, restaurants, music venues and other public spaces.