TOKYO (Kyodo) -- Rieko Nakagawa, author of the long-selling picture book series featuring twin mice "Guri and Gura," has died, the publisher of many of her books said Thursday. She was 89.

Children's literature author Nakagawa died of old age at a hospital in Tokyo early Monday morning, according to Fukuinkan Shoten Publishers Inc.

Born in 1935 in Sapporo in Japan's northern main island of Hokkaido, Nakagawa began writing while working as a nursery school teacher.

She published her first children's book, "No No Nursery School," in 1962, depicting stories of a nursery school boy named Shigeru.

"Guri and Gura," which debuted in 1963, has been translated into 14 languages, published in 13 different countries and regions outside of Japan, and is especially popular in China and South Korea, the publisher said.

Nakagawa also wrote the lyrics of the popular opening track for Studio Ghibli's classic anime film "My Neighbor Totoro," titled "Sanpo" and known as "Hey Let's Go" in English.

Nakagawa's younger sister and illustrator, Yuriko Yamawaki, who also went by her maiden name, Yuriko Omura, drew pictures for "Guri and Gura" and many other stories by Nakagawa.

The sisters received the Kikuchi Kan Prize in 2013 for their achievements in cultivating sensitivity and imagination among children through their many collaborations.

Yamawaki died at 80 in September 2022 due to an immune system disorder.