Why is Ukigumo regarded as the first modern Japanese novel?

Ukigumo (1887–89), written by Futabatei Shimei, is widely regarded as the first modern Japanese novel primarily because it pioneered the use of the modern colloquial idiom in Japanese literature.12

Influenced by his study of Russian literature and contemporary Western literary criticism, Futabatei employed a style known as gembun itchi—the unification of spoken and written language. This was a significant departure from the classical Japanese literary language and syntax that had dominated traditional writing. Futabatei was convinced that the colloquial tongue was the only appropriate medium for accurately describing the writer’s own society.231

Furthermore, the work is noted for introducing modern realism to the Japanese novel. Through its protagonist, Utsumi Bunzō, the story explores the psychological and social struggles of an individual attempting to navigate the rapidly modernizing environment of late 19th-century Japan, marking a shift away from the didacticism often found in earlier Japanese fiction.312