Why are so many Japanese characters the same as those in China?

Because Chinese characters were introduced to Japan in ancient times, Japan created its own characters on the basis of Chinese characters.

Since BC, Chinese characters, as an important part of Chinese culture, have spread to the Korean peninsula and Japanese islands with strong radiation together with metallurgy, textile, farming and other civilizations, forming a continuous Chinese character cultural area.

According to historical records and Japanese archaeological discoveries, Chinese characters were introduced into Kyushu and Fukuoka in Japan through Liaodong and Korea in 1 century BC. The seal script and official script of Chinese characters were mostly introduced into Japan in the form of engraving on bronze mirrors. Like other patterns on bronze mirrors, these characters are regarded by the Japanese as symbols of solemnity, sacredness and good luck. Since then, while copying bronze mirrors, Japan has also begun to copy China inscriptions.

After Chinese characters were introduced into Japan, they not only became public servants to record historical facts, but also became the only official writing in Japan at that time.

Extended data:

In ancient times, Chinese characters were the only international communication language in East Asia. Before the 20th century, it was still the official written standard language of Japan, Korean Peninsula, Vietnam, Ryukyu and other countries, and all East Asian countries created their own Chinese characters to some extent.

In the non-Chinese character system, the Japanese themselves simplified Chinese characters and formulated new Japanese fonts; Vietnam, North Korea, Mongolia and other countries that used Chinese characters in history have now abandoned Chinese characters.

This feature of Chinese characters plays an important role in maintaining a cultural circle-a nation full of various dialect groups that cannot communicate.

Baidu Encyclopedia-Japanese Characters