Yoshiro was an expert on Japanese Nestorianism. Saeki theorised that the Hata clan, which arrived from Korea and settled in Japan in the third century, was a Jewish-Nestorian tribe. According to Ben-Ami Shillony, "Saeki's writings spread the theory about 'the common ancestry of the Japanese and the Jews' (Nichi-Yu dosoron) in Japan, a theory that was endorsed by some Christian groups."[17]