Since the Southern Dynasties of ancient China, Japanese eagerly studied the advanced culture and technology from the Chinese nation. Japanese was called “Wo” (倭) by Chinese. Japanese kings paid tributes to the emperors of China every year, and the emperors conferred titles on them. The Japanese nation was a clever people, and they were eager to excel other nations. When they comprehended the culture of the Chinese nation, they found the name and status of their nation were not well. So Japanese wanted to show their self-respect to the Central Nation. They started to call their country "Nippon" (日本) which means the land of the rising sun.
In A.D. 593, Shotoku Taishi (聖德太子), an important statesman of Japanese history, started to assist his aunt, the female king Suiko (推古), in governing Japan. Shotoku Taishi was very eager to study Chinese culture and model his country after China. In 603, Shotoku established a system that Japanese official vestments used the style of Chinese official vestments. In 604, Shotoku enacted the Seventeen-Article Constitution, and consolidated the centralism that Japan was ruled by a king. Then Shotoku Taishi wanted to show his self-confidence to Chinese.
In 607, Shotoku sent Onono Imoko (小野妹子) to visit China and deliver a letter to the emperor of China. At that time, China was ruled by a tyrannical emperor, Sui Yang-Emperor (隋炀帝) who was the second emperor of the Sui Dynasty. When Sui Yang-Emperor read the beginning of the letter, he became very angry. Why? The beginning of this letter said, “The Heaven-Son of the land where the sun rises greets the Heaven-Son of the land where the sun moves down.” (日出处天子致书日没处天子无恙)
This was a seriously diplomatic provocation.
“Heaven-Son” (天子) was the sacred title of the supreme monarch of the Central Nation, and Chinese thought there was not another emperor (皇帝) in the world except their own emperor. In Japanese historical books, they called all of their supreme monarchs “Heaven-Emperor” (天皇), but in fact, before the Tang Dynasty, the title of the Japanese supreme monarch was “King” (王). In 674, Tang Gao-Zong (唐高宗), the third emperor of the Tang Dynasty, enacted a statute that the title of emperor was "Heaven-Emperor" and the titile of empress was "Heaven-Empress" (天后). Japanese students brought the title “Heaven-Emperor” to their king. However, when Japanese visited China or studied abroad, they didn’t dare to call their supreme monarch “Heaven-Emperor”, and they had to call their supreme monarch “King”. In ancient Chinese historical books, all of the supreme monarchs of Japan were called “King” all along. The Roman Empire was the greatest country in the West, but Chinese still called Roman emperors “King”. The sacred title “Heaven-Son” was from the great Zhou Dynasty. People called the kings of Zhou Dynasty “Heaven-Son” and “Heaven-King” (天王). Which foreign monarch dared to call himself “Heaven-Son”!
Chinese thought the sun rose in the east divine tree Fusang (扶桑) and moved down in the west extreme. So Japan was also called “Fusang” by Chinese. But Chinese never thought the sun moved down in the Central Nation. According to Chinese thoughts, the down sun presaged decline and death.
These were why Sui Yang-Emperor was very angry. Originally, the emperor wanted to kill Onono Imoko and his attendants. At that time, the king of Koguryo (高句丽, a country in the North Korea) was irreverent to Sui Dynasty, so Sui Yang-Emperor was preparing to punish Koguryo. The emperor thought again and again, and finally he decided to forgive the Japanese and permit to establish diplomatic relations with Japan, in order to get the support of Japan in the later war of attacking Koguryo. Sui Yang-Emperor was a temperamental man and killed many persons, but Onono Imoko luckily escaped from danger because of the tense situation between the Central Nation and Koguryo.
In 608, Sui Yang-Emperor sent Pei Qing (裴清) to visit Japan with Onono Imoko. The female king of Japan led several hundred attendants to salute Pei Qing. Maybe Onono Imoko told his king that the emperor of the Central Nation was very angry, Suiko apologized to Pei Qing and said, “I know the great Sui Empire is a country of propriety and righteousness, so I sent an envoy to pay tributes to your country. We are uncultured, so we don’t know propriety and righteousness. I hope your country will be willing to civilize us.” Pei Qing said, “The Emperor know your sincerity, so I was sent to instruct you.” The female king Suiko was very pleased, and ordered many attendants to escort Pei Qing to return the Central Nation and pay tributes to the emperor of Sui Dynasty.
These historical records were mainly from the authentic historical works “The History of Sui” (隋书) which was written in the Tang Dynasty. The historical books of Japan tried to create a historical system that all of Japanese emperors were from the same lineage. In fact, many Japanese scholars preferred ancient Chinese historical works to ancient Japanese historical books.