Japan, who will host the Rugby World Cup next year, are due to play against New Zealand and England next month and Joseph said those sides would provide tougher tests than any his team had previously faced.
Joseph would not be drawn on reports that Japan could be included in an annual tournament featuring the top 12 countries but said playing against high-quality sides was the best way to develop the national side.
"I think where Japanese rugby sits, it is crucial that we have a stronger brand of competition than the Top League to develop the national game," said the New Zealander at a news conference in Tokyo.
"If we only had the Asian tournament (Asia Rugby Championship) and the Top League to develop our players to an international level, then it would be very difficult to achieve great things at test level."
Joseph has been critical of the domestic Top League in the past and will be pleased that a shortened season this year will allow him over nine months to work with the players in preparation for the World Cup, which starts on Sept. 20.
Joseph's wish for Japan to test themselves against the best will be granted in November when they play world champions New Zealand in Tokyo on Nov. 3, followed by a trip to Twickenham to face England two weeks later.
Despite the step up in class, Joseph said there would be no tinkering with strategy.
"I don't think our gameplan changes a hell of a lot. We are playing better opposition than we have ever played before," he added.
"The All Blacks have a win record of over 90 percent I think so they are a difficult team to beat, as we all know.
"The All Blacks and England ... will really attack our set-pieces and try and overwhelm us from the set-pieces, and that is a challenge that we are going to get in the World Cup as well, when we play Ireland and Scotland."
Joseph named a 35-man squad for the two tests on Monday and included three players looking to earn their first cap.
Stalwart Michael Leitch will captain the side.
(Editing by Peter Rutherford)
