Koganemaru is considered to be the first modern book for children in Japan. It was the first volume of Shônen Bungaku [Juvenile Literature] series (32vols) by Hakubun-Kan. Iwaya said that this work for children was "of quite a new phenomenon in the Japanese literary world."

  The protagonist is Koganemaru, a dog, whose father was killed by a tiger. Koganemaru searched for the tiger and, with the help of his friend, another dog, succeeded in avenging his father's death. The amusing idea of a dog's revenge story, the eventful plot, and word-play inserted in many places had a strong appeal to readers.

created a big sensation among literary people, as it was the first novel-length story originally written for young readers. Many reviews of this book appeared in newspapers and magazines. Most of them favored it, but Hori Shizan in the Yomiuri Newspaper criticized that this book should have been written in a colloquial style, not in a classical literary style. Iwaya retorted that he used the classical style to make it easier for young people to read. In the twelfth edition in 1899, several changes were made.

  In 1921, Sanjûnenme: Kakinaoshi: Koganemaru [30 Years After: Re-Written Koganemaru], a colloquial style edition, was published. A reprint of the original edition was published by the Museum of Modern Japanese Literature in 1968.