TOKYO — Ryuichi Kawamura is not only famous as the lead singer for Luna Sea, one of Japan’s most popular rock bands. He is also a respected watch collector, with frequent appearances in the country’s watch-related media and at events organized by Tokyo’s tight-knit watch community, and has an Instagram account featuring the timepieces he wears each day.

Mr. Kawamura, 51, made his debut with the band when it formed in 1986 in Kanagawa prefecture, just south of Tokyo. It started out as visual kei — Japan’s answer to glam rock, with flamboyant costumes and hairstyles — but toned things down in the 1990s and now has turned to an edgy rock style, with the occasional animal print.

Like the band’s musical style, Mr. Kawamura’s taste in watches has evolved, too. “I enjoy all kinds of watches; there are no boundaries,” he said in a recent interview at Chrono Theory, a Tokyo boutique that features independent watchmakers.

“At the beginning I focused on just a small part, just the best and most expensive ones,” he continued. “But gradually, I got interested in the things that could become the best. It’s like Cinderella turning into a princess in the end; it’s the things on the trajectory to become the best that I’m more interested in now.”

Mr. Kawamura said he had become attracted to watches that could cost as little as 5,000 or 10,000 yen, the equivalent of $44 to $89. “Recently I bought a Citizen Solar watch,”
he said. “It was only ¥5,000, but it’s such an interesting watch with a good design. It’s not only about the price.”

For high-end purchases, Mr. Kawamura often shops at the Hour Glass, a boutique in the Ginza district of Tokyo.

“He’s a superstar here,” Atsushi Momoi, the store’s managing director, said, referring to both the singer’s public profile and his status in the store. “Mr. Kawamura has been a customer here since 2002, when the boutique was first established in Tokyo.” At the time, Mr. Momoi managed Mr. Kawamura’s purchases, including a Patek Philippe Minute Repeater, which was difficult for Japanese to obtain then.

“Over the past 20 years, his passion for watches has only increased,” Mr. Momoi said. “But recently, his taste got wider; he opened his eyes wider.”

In September, to celebrate its 25th anniversary of doing business in Japan, the boutique released the Ulysse Nardin Classico The Hour Glass Ginza 25th Anniversary edition in a 25-piece limited edition. The timepiece is equipped with a 22-karat gold rotor on the back and a salmon-pink dial finished with a radial guilloché for a 3-D effect, and with Breguet hands and numerals. Mr. Kawamura purchased one, but had the original crocodile leather band changed to a silver metal bracelet.

Mr. Kawamura began collecting watches about 25 years ago, when he received a 1940s Breitling Navitimer Chronomat Venus from one of his mentors, Hideki Saijo (known for his Japanese rendition of the Village People’s “Y.M.C.A.”).

“That was the start. That’s when I began collecting watches,” the singer said. “Back then, people around me used to always tell me, ‘You need to own one good watch in your life.’”

His collection has expanded to more than just one good watch, although he will not reveal how many he has now. (“I always say that I only keep eight watches total,” he said. “If the number is too high, people might say, ‘Why do you need so many watches? What do you use them for?’”)

Mr. Kawamura brought 11 timepieces to the interview — and said he could not name a favorite from the selection, which included a rare platinum A. Lange & Söhne Cabaret acquired on a visit to the factory in Dresden, Germany; an Audemars Piguet Royal Oak Jumbo Extra-Thin in pink gold; a Patek Philippe Nautilus Ref. 5711 in rose gold; a platinum Patek Philippe Ref. 5140 Perpetual Calendar and a limited-edition Maurice Lacroix x Label Noir.

“Usually, people only need one watch to wear, but after I got one, I started thinking about getting more because I want to be able to choose according to my lifestyle,” he said. “That’s why I can’t choose just one.”

His most treasured pieces include some customized Patek Philippes, such as the Grand Complications Ref. 5160 Perpetual Calendar with Moon Phase. “Only the white dial was available, but I asked Patek Philippe to customize it to a black dial,” he said. The white gold case was engraved by hand with an intricate floral pattern, and the hunter case back opens to reveal the movement. (Again, he customized the strap, changing it to a dark purple leather Jean Rousseau model with a contrasting silver stitch.)

When Mr. Kawamura wears a suit, he sometimes accessorizes it with his Vacheron Constantin Patrimony Skeleton, which he bought in the 1990s. “When I first entered the store, I saw it and loved it immediately,” he said. “You can see the movement very clearly.” He outfitted the watch with a Jean Rousseau gray leather strap lined in red. “You can see the red peek out when I wear it. It has a playfulness to it,” he said.

Recently, Mr. Kawamura actually designed a watch: a Quai des Bergues Verse o’Clock model by the Geneva-based brand Czapek, a project orchestrated by a fellow collector known only as Chrono Peace for sale at Chrono Theoryin Tokyo.

The 10-piece limited-edition watch (¥2.8 million) was engraved with Mr. Kawamura’s name on the case back and featured fleur-de-lis white-gold hands and a terra cotta dial. “This was the first time I designed a watch, so I was really nervous,” he said, “but the result is very good.”

Xavier de Roquemaurel, chief executive of Czapek, said in an email: “This timepiece illustrates Czapek’s art of creating unique bespoke watches. We deeply listened to Ryuichi’s ideas and strived to create a watch that represented his very personal style and music.”

Currently, Mr. Kawamura is on tour in Japan with Luna Sea, which disbanded in 2000 but reunited 10 years later. As he is performing regularly, he said he found the Formex Essence Leggera automatic chronometer, with a case made of carbon fiber and ceramic bezel and crown, fits his needs. “It’s extra light, especially for a mechanical watch; it weighs only 50 grams,” or almost 1.8 ounces, he said, displaying the model outfitted with a fabric strap.

As for future projects, Mr. Kawamura said he was in no hurry to decide. “It’s about the same as watches: If you take your time and spend a lot of time crafting a watch, you can make a great watch. My music career as well.”