Xiao Riben is a derogatory Chinese slang term for the Japanese people or a person of Japanese descent. Literally translated, it means "little Japan" or "little Japanese". It is often used with "guizi" or ghost/devil, such as "xiao Riben guizi", or "little Japanese devil".
This is a largely archaic term used in China as a result of the Sino-Japanese Wars in offense to the Japanese forces at the time.