Japan beat Hong Kong 49-8 in Tokyo at the weekend to clinch the Asian Five Nations title and also assure their safe passage through to the World Cup.
They join South Africa, Scotland, Samoa and the United States in Pool B of the 20-team competition in England next year.
The Boks will face Japan in Brighton on September 19, while their other group games are on September 26 (v Samoa, Birmingham), October 3 (v Scotland, Newcastle) and October 7 (v USA, London).
It will also see the Boks come up against Eddie Jones, who coaches Japan. Jones was a coaching consultant to Jake White when the Boks won the 2007 World Cup in France.
Meanwhile, according to the BBC Sport website, Hong Kong could still make the World Cup despite their loss.
For that to happen they must come through the four-team repechage event.
If Hong Kong were to beat Uruguay in the first round, they would then face either Russia or an African team in the final. Should they win that, they would secure the last place in Pool A alongside England, Wales, Australia and either Fiji or the Cook Islands.