Three years ago, Nancy Miah had never heard of the fictional, Dutch, poker-faced bunny known as Miffy. Now, she calls herself the “Miffy Queen.”

Every time Ms. Miah, a content creator in New York, visits Amsterdam with her Dutch boyfriend, she stocks up on Miffy products. “I would buy a bunch of Miffy stuff, and people would ask, ‘Where did you get that, what is that?’” she said.

Now her friends, who previously had zero interest in collecting cute characters and toys, are obsessed with Miffy merch. “I have friends who are big fashion heads who don’t care about kawaii culture at all,” Ms. Miah, 28, said. “They’re like ‘Oh, can you pick me up a Miffy plushie when you come back from Amsterdam next time?’”

Miffy was created in 1955 by Dick Bruna, a Dutch artist and author. She is the star of a series of picture books and a familiar character in many European and Asian countries. (In the Netherlands, she’s known as “nijntje.”) Until recently, she was largely unknown in North America, where most children did not grow up reading her books, watching her on TV or seeing her merchandise in stores.

But over the last year, Miffy has become ubiquitous in America. She’s on TikTok and Instagram, dangling from key rings and glowing as giant floor lamps. On Pinterest, she adorns nail art, stares out from the back of phone cases and nestles on beds in various plush forms. Google searches for Miffy in the U.S. have never been higher, increasing by 210 percent from 2022. And on TikTok, the hashtag for Miffy earned more than 400 million views in the last year, with America accounting for over a quarter of those views.

The hordes of new Miffy fans, buying and showcasing their merch online, are more often than not young adults who want to inject a little joy — and childhood — into their daily lives. They are challenging the idea that cute characters meant for kids have an age limit. As one TikTok creator put it in a caption underneath a video of her unboxing a Miffy floor lamp: “I love having adult money, so I can spend it on kid things.”

In 2020, when Ms. Miah began posting her Miffy collection on TikTok, she frequently had to explain who the character was to her followers. Ms. Miah is a part of the kawaii community on TikTok, where cute characters reign supreme. While her followers were well-versed in Hello Kitty lore and the creatures of Studio Ghibli films, Miffy was new for many of them.

In the past year, Ms. Miah’s following has doubled, and her Miffy-related videos draw the most views. Many of her new followers come from outside the kawaii community, she said, including people interested in home goods, fashion and interior design.

Before 2019, most of the efforts to market Miffy in North America were catered toward young children, highlighting her literary heritage, said Debra Joester, the president and chief executive of Joester Loria Group, an agency that licenses Miffy in North America.

“Most literary brands start when you’re very young,” Ms. Joester said, “and then there’s that nostalgic factor of wanting to continue with the characters, and the art, that you fell in love with as a young child.” In America, she said, that was “not the case with Miffy.”

So the company shifted its marketing strategy to focus more on aesthetics, promoting Miffy as a character with a versatile, classic design that translated well on everything: children’s apparel, accessories and home goods. In 2022, the success of a Miffy collaboration with Hanna Andersson, a children’s clothing brand, led to more retailers wanting to stock Miffy goods. This was a turning point, Ms. Joester said. Miffy merchandise sales in the U.S. shot up 435 percent in 2022 and have continued to grow since.

This year, Miffy had a little bit of lunar luck as well — 2023 is the Year of the Rabbit in the Lunar New Year. High profile brands like Mulberry and Tommy Hilfiger partnered with Miffy on limited edition collections, introducing her to new audiences. At the same time, Gen-Z TikTok creators continue to popularize Miffy, highlighting items they’ve collected and spotlighting shops selling Miffy merch.

In the U.S., Miffy products are still relatively hard to find — which may be part of the appeal. “Miffy feels very new for Americans,” Ms. Joester said. “I think part of what Gen Z does love is that act of discovery — when they see something that isn’t broadly out there and they can start making it their own.”

More products specifically targeting Gen Z — including apparel, home goods and accessories — will roll out next year in the American market in stores like Urban Outfitters. On a recent trip to the mall, Emma Salehi, a college sophomore in Los Angeles, spotted a Miffy shirt at Uniqlo. “All the girlies at my school — I’ve seen three people so far wearing that shirt within the span of a week,” Ms. Salehi, 18, said.

The interest in Miffy among American adults points to a broader shift in spending habits and attitudes toward toys, both of which have changed since the Covid-19 pandemic. “There’s a big bump in purchasing power from them within toys and plush — all these things that would typically be bought for kids, they’re buying for themselves,” said Erin Rechner, referring to adults. She is the head of kidswear at WGSN, a trend forecasting company. “In the Asian market, that’s already something that’s ingrained in the culture, where adults are buying similar items that their kids and youth are interested in,” she said.

Fiona Harkin, a foresight editor at the Future Laboratory, a trend forecasting company, referenced Japan’s well-established kawaii culture, and how that concept is becoming more and more embraced in the West.

“I think people do look for comfort and simplicity, and most of the time we find that in our childhood — Miffy is a great character for that, especially with the slightly blank face,” Ms. Harkin said. “It says an awful lot about how you can project onto that character — it’s very clever.”

But for many Miffy enthusiasts, the reason they’re drawn to the character is a simple one: She adds joy to the mundane.

This summer, Elle Wedel, a student and content creator from Toronto, shared a video of herself — one of her most popular TikToks — repurposing a Miffy soap dispenser into a makeup-remover dispenser. “Some people might say that it’s a bit frivolous, but personally I think that anything that can brighten your day, or simple tasks, just by existing can make a huge difference,” Ms. Wedel, 21, said.

Miffy’s typically neutral color palette and simple design also blends in well with different aesthetics. “She can be incorporated into day-to-day items in a more subtle way, but it’s still a little bit of joy sprinkled in there,” Ms. Wedel said. “That’s kind of unique to Miffy.”