It was only in recent Chinese history that people started to claim that Xu Fu was the ancestor of the Japanese. This is motivated by Chinese nationalistic pride.
The problem is that 秦 could mean any early immigrant from China, not just Xu Fu, and this is generally how the origin of the surname Hata has been interpreted (i.e. 'Hata' is a generic label for descendants of immigrants from 'Qin', i.e. China).
The Xu Fu legend probably wasn't Chinese at all, but a Japanese one. Nihongi was the first source which hinted this. The Hada(Qin ren) which resided in Western Aya wasn't just a name that referred to all Chinese; they were directed to a specific prestiged group who claimed to be descended from Qin Shi Huang. The other Chinese were known as Han ren, not Qin ren. It was the Japanese which brought this legend to China during the five dynasties period under the monk Hong Shun probably around 927 AD. Since the Nihongi and this claim were somewhat related, I suspect that the legend was formed in Japan even prior to the 10th century. Its most probable that the Japanese at the time simply made up the Xu fu legend after examining Shiji and Hanshu to enhance their prestige as typical for many "Dong Yi" of the time. From an examination of Nihongi we know that many speeches made by these early Japanese emperors such as Tennu Jimmu were words taken right out of the mouth of Han Gaozu in Shiji and Han shu.
The popularization of Xufu as ancestors of at least a major portion of the Japanese population in modern times is not just a Chinese claim, but was made by a number of Japanese historians as well in the mid-20th century. In fact mainland China seem to be quite late in the reception of this theory.(Being prevalent in Hong kong, Taiwan and Japan first). The previous Japanese prime minister Tsutomu Hata also openly announced to the public that he was descended from Qin Shi huang through Xu fu.(I suspect that this might have political reasons).
Regarding the "legends" of the Japanese in ancientChinese written accords, Wei Zhi - Dong Yi Chuan (Official history of Wei, about Eastern Strangers, /Gishi-touiden/ -- jp, or known as /Gishi-wajinden/) reports about Japanese in AD 3c. Beside a description of the female governor and the tattooed faces of men, there is a part that says, "When asked, everyone answered they were descendants of TaiBo of Wu. Sima Qian also wrote that "wrote that Xu Fu said to Shi Huang Di of Qin, that he was leaving for the Eastern Sea to search for a medicine for eternal life in Fenglai islands, which the Chinese people consider to be Japan. He left with about 3000 people, but didn't come back because he became the king there. Certainly, we would view such written accords with skepticism since it appears to be written by speculation more than actual facts (people wrote what they know and certain the two Chinese writers had limited access to extremely limited sources of information back then).
The original source can be found in Jin Shu, Biography of the Four Yi:
This just gives more evidence to the fact that the Xufu was just a later legend since the original Wo people claimed to be descended from Taibo! Since many Japanese probably immigrated from the Wu region, that might be where the story originated(since Wu was also said to be founded by Taibo).
Edited by Borjigin Ayurbarwada, 09 August 2008 - 11:10 PM.