HIGASHINE, Japan — Yamagata Prefecture, in the north of Japan’s main island, Honshu, is known for its cherries. And when you disembark at the Sakuranbo-Higashine train station, they won’t let you forget it: There are large posters of cherries, a cherry-shaped monument, a cherry-themed souvenir shop and even images of cherries affixed to the train itself.

But Higashine has more than just cherries. It is where many of the Casio G-Shock watches come to life. It was the dream of its creator, Kikuo Ibe: a watch whose case and movement would never break.

In April, the chunky and durable G-Shock — the focus of so many enthusiastic watch forums — will turn 40. I decided to visit the factory to see how it was created.

So how does Mr. Ibe feel now that his baby is reaching middle age?

“The original target users of the first G-Shock were people working hard outside,” he wrote in an email. “The success as it is now was entirely unexpected and surprising.”

Mr. Ibe, 70, still works at the company’s research and development center in Hamura, a city in the Tokyo area, so it was natural for him to add: “We hope you’ll be looking forward to the evolution of G-Shock in the future.”

Certainly the model’s fans are. As Andy McIntyre, a British collector who posts on Instagram as @gshockin17, wrote: “It’s a relief to keep it simple and appreciate a watch for being a watch! Why would I look on my phone for the time when I can soak in the details of a G-Shock and that classic screen?”

Casio and G-Shock

At first, my visit to Yamagata Casio, as the factory in Higashine is called, seemed a lot like stops at other large Japanese watch manufacturers: I had to take off my shoes and don slippers, watch a presentation on the company and walk along what seemed like endless long halls. Except the whole experience was infused with a lot of playful good humor, a Casio hallmark.

Shinichi Kimura, president of Yamagata Casio, welcomed me with fun facts about the prefecture. (Did you know fried chicken consumption per capita in Yamagata is the highest in Japan, with 64 pieces per month? Or that the prefecture holds a Guinness World Record for the most soup — imoni nabe, a hotpot dish — served in an eight-hour period?)

The prefecture’s connection to the first G-Shock was part of the recitation: “The history of G-Shock is the history of Yamagata Casio.”

And both are woven into the history of its parent, Casio Computer Company, a multinational electronics manufacturing corporation that, among its many products, produced 38 million watches in the fiscal year that ended March 31, 2022, and reported watch sales of 152.3 billion Japanese yen ($1.1 billion) — making it Asia’s largest watch manufacturer by sales.

Yamagata Casio is among its subsidiaries. The factory covers 30,701 square meters (a little more than 7.5 acres) in seven vast buildings; it was established in 1979 and the newest building was constructed in 2018.

Its 600 employees make a variety of products, including projectors, calculators, medical devices, hand-held scanners and watches, including the higher-end G-Shock MR-G models and the Oceanus. Since 2020, it also has made employees’ surgical masks with (you guessed it) a cherry motif.

The inexpensive G-Shock models, which range from about $150 to $300, are made in three factories in China and one in Thailand.

G-Shock Playtime

Mr. Kimura said that when Yamagata Casio is charged with making a new watch model, like the G-Shock MTG-B3000 that was introduced in May, it receives blueprints from the R. & D. operation in Hamura. Its staff members then make the needed molds and use them and the production robots to produce the model’s parts, make the quartz watch movements and even ship the finished watches.

The factory’s staff also supervises production of various pieces in the other factories (“I can watch the machines from my computer,” Mr. Kimura said) and workers can be dispatched to take care of any problems that arise. “By doing that, we can maintain the quality,” he said.

When it comes to the high-end watch models produced at the Yamagata factory, “G-Shock are man-made,” Mr. Kimura said — or, more accurately, woman-made. “The current assembly team is composed of approximately 30 people; all of them are women.”

Not just any worker can join the assembly team; each one has to complete a series of tests in a medalist system (achieving gold, platinum and Meister, the top medal status). “They’re the best ones in Yamagata,” Mr. Kimura said of the assembly team members. “They’re patient and dedicated.”

The G-Shock MTG-B3000, which retails from ¥121,000, was being assembled at Yamagata Casio during my visit (each work day focuses on a different model). MT-G stands for Metal Twisted G-Shock, a name that emphasizes the highly shock-resistant nature of its carbon-resin case with interlocking metal parts.

The visit started in the showroom, which displays some of the company’s watches and the production technology used to make them. Groups, such as those from local schools, are welcome to visit by appointment, but it is not open to the general public.

There also were machines used to test timepieces for endurance, vibration and shock resistance — a sample of those used at the Casio main testing center in Hamura.

In the Yamagata showroom, I threw an egg onto a shock-absorbing mat made with Alpha Gel, a soft silicone gel that adds shock absorption and vibration damping to G-Shocks (the egg didn’t break). I also admired a vertical fish tank where fish swim among G-Shock watches (the fish are fed every morning) and posed with a 5-foot-tall plastic figurine of the G-Shock mascot (its head is shaped like the face of a G-Shock).

From the showroom windows, I could see the production lines, as well as the assembly table, which was in the shape of a capital G, of course. But before a G-Shock is assembled, the parts are produced in the adjacent area: the factory.

Meet the Robots

The automatic timepiece movement assembly line is where the clean-room tour started. I slipped into a head-to-toe blue dust suit, with tall blue boots that zipped up around the calf, and then went through an airlock. Ryohei Saito, a manager in a section of the Timepiece Manufacturing Technology Department, led me around the factory, noting that its automated functions operate 24/7.

I saw some machines churning out tiny plastic gears and rotors that automatically were moved by conveyor belt around the production line toward their ultimate assembly into movements. One machine ensured that the pieces were the right side up. “It also inspects the angles and sides, and gets rid of defective parts,” Mr. Saito said.

“The machines are all made in Japan by Casio,” he said, pointing out the Casio name on each one. One had the general appearance of a dog, complete with a red light on the tip of its tail and two blue ears.

“Engineers can play with the shape of the machines,” Mr. Saito said. “The machines are functional but playful.”

On the floor, the perimeter of the machine area is outlined in strips of silver metal. “That is the earthquake protection system,” he said, explaining that 1,755 anti-seismic plates under the flooring keep the ground stable whenever the area’s frequent earthquakes hit. In March, for example, the company said that a magnitude 7.4 quake hit nearby Fukushima, but the factory’s machines were not affected.

Becoming G-Shock

I stepped into the next room, the premium timepiece production line, the one outfitted with the G-shaped assembling module.

Tadakazu Yuki, a manager in another section of the manufacturing technology department, and Masaki Nakano, a general staff member of the same department, led me around the area. “The assembly begins inside the G and follows shape of the letter,” Mr. Nakano said.

About 30 women in their early 20s to 40s, all wearing protective suits, were standing at the G-shaped table. As I walked around, I saw them performing the various steps that go into assembling the MTG-B3000 model: module assembly (the seven screws that are screwed in the movement), solar panel and dial installation, adding the hands to the movement (there are eight hands on that model), hand positioning and angle adjustment, hand height adjustment, installation of the hands and fitting of the case. “Assembling G-Shock is a combination of human skills and machines,” Mr. Nakano said, and the team’s production capacity is said to average about 8,000 watches a month.

Once assembled, a G-Shock still isn’t ready for sale, as it must be tested for things like water resistance, airtightness and durability, depending on the model. “If the watch fails a test, it will be repaired,” Mr. Nakano said. Each high-end G-Shock watch also is inspected; lower-grade ones are not.

After a staff member attaches the strap, there is a final check and the watch then is ready for shipping.

Back to 1983

Last came the real treat: one of the first 1983 G-Shocks (there are only a few of them, kept in the Hamura office, but one was brought over for my visit). I wore it on my wrist and was surprised to see it didn’t look old or much different than current G-Shock models — the definition of timelessness.

In 2017, the company produced its 100 millionth G-Shock (the empty sake barrel from the celebration is in the Yamagata lobby). By 2021, that number had reached 140 million.

“G-Shock is so popular, it’s often imitated,” said Mr. Shinichi, the president of Yamagata Casio, as we finished the tour. “But in the shape of G-Shock there is a beauty that cannot be imitated.”