When did the Japanese start using pseudonyms?

In the past, some people in Japan could speak Chinese, but compared with their own language, it was also a foreign language. Only some nobles could understand it, while civilians did not know Chinese characters and could not speak Chinese. Around the 5th century AD, the Japanese people created a brand-new syllabic script based on Chinese characters, which was greatly simplified compared with China's double-character spelling (Dong = De D, Hong ong, Qie), which enabled Chinese characters to spread in the lower classes of Japan, but Chinese characters were complicated and difficult to understand, so Chinese characters were replaced by pseudonyms (mostly street performances and rap texts) in folk circulation. With the popularity of pseudonyms, pseudonyms and Chinese characters complement each other, thus forming. Of course, the pronunciation of Japanese can't be exactly the same as that of China, and the pronunciation of Chinese characters is also changing, so the pronunciation difference between the two countries is getting bigger and bigger.