TOKYO — At age 36, Hello Kitty may be running out of product lives.

That is the fear of executives at the Sanrio Corporation, the Japanese company that created the cute, cartoonish white cat in 1974, and groomed her into a global marketing phenomenon worth $5 billion a year.

In Japan and around the world, Hello Kitty has been licensed over the years for products that include dolls, clothes, lunch boxes, stationery, kitchenware, a Macy’s parade balloon and even an Airbus owned by Taiwanese airline EVA Airways. But amid signs that Hello Kitty’s pop-culture appeal is waning, especially at home, where sales have shrunk for a decade, the company has struggled to find its next-generation version of adorable.

Sanrio’s other flops include Spottie Dottie, a pink-frocked Dalmatian, and Pandapple, a baby panda. Even the moderately successful My Melody (a rabbit) and TuxedoSam (penguin) show no signs of achieving global Kitty-ness.

“We badly need something else,” said Yuko Yamaguchi, who has been Sanrio’s top Hello Kitty designer for most of its 36 years. “Characters take a long time to develop and introduce to different markets,” Ms. Yamaguchi said. “But Kitty has been so popular it’s overshadowed all our other efforts.”