In the heart of rural Chiba, the Kisarazu Costco branch is doing brisk business. No music plays, but inside the immense warehouse, demonstrations are underway and samples are being handed out.

The atmosphere is buzzing. Under the watchful eye of Ken Theriault, Costco representative director and Japan country manager, the American membership-model wholesaler has flourished in Japan.

Founded in 1983, Costco is the third-largest global retailer. Japan is its fourth-largest market by store count.

Stocking everything from gold bars to toilet paper, fresh fruit to pizza and sushi, it offers Japan something of a unique experience.

Theriault works across all aspects of the business. He likes to be on the move and keep staff on their toes. We begin talking at Costco¡¯s nearby office, stopping briefly on a floor where bacon-stuffed bread is being measured and sampled. Then we head into the supermarket.

As we cut our way through the mega-sized produce, he jokes with staff, inquires about a particular product and spies a tiny piece of trash on the shiny floors and quickly picks it up. He tells an employee to get a broom.

With a busy schedule to keep and mounting traffic, Theriault hands me one of Costco¡¯s famous inflation-proof ?180 ($1.20) hot dogs to go ¡ª and suggests we continue the interview on the road. As the Costco storefront shrinks in his car¡¯s rearview mirror, he talks about how he came to Japan and built the business here.

Affable and energetic, Theriault is from a large Canadian family. It was one of his sisters who nudged him toward his current career, suggesting that a smart haircut would help his job prospects. She was tragically killed in a car accident, perhaps a part of why Theriault ¡ª who crisscrosses the country to carry out surprise store visits ¡ª is such a careful, accommodating driver himself.

Over the years, Theriault steadily worked his way up the business, and in 2009 he and his family made the 10,700-kilometer leap from Canada to Japan to lead Costco in the country.

¡°It was literally seven days a week, 18 hours a day,¡± he said, recalling the early adrenaline-fueled days.

¡°To get open was tough, to hire people was tough, but it was a never-give-up attitude.

¡°Now I sit back and we¡¯re going to have our 37th building opening in 26 years, we have 14,000 employees, two depots, e-com. It¡¯s pretty good,¡± he said of the brand¡¯s Japan presence.

But Theriault is far from complacent, viewing ¡°everyone¡± as a competitor because of Costco¡¯s range of product categories. Expansion plans are informed by data maps showing car and home ownership, and also a desire not to cannibalize existing stores. The aim...