The Song Dynasty's "Qingbo Magazine" records: "A Japanese ship was stranded in the Song territory. There were about twenty people on board. The Japanese women all had long hair. When they encountered handsome men from the Central Plains (China), they would choose the most handsome and offer themselves to them for the purpose of having intercourse, which was called 'Du Zhong' (improving the race)."
This record says that Japanese women came to China during the Song Dynasty, and upon encountering handsome Song men, they would willingly have intercourse with them with the aim of giving birth to offspring to improve Japan's population.
(Note: Historical records should be viewed critically as they may reflect biases or inaccuracies of their time.)