World Rugby chairman Bernard Lapasset says Japan should be included in the Sanzar showpiece.
The sport is enjoying a surge in popularity in the country after the Brave Blossoms won three out of their four pool matches at the 2015 World Cup, including their toughest fixture against the Springboks.
A Japanese franchise, the Sunwolves, will also enter an expanded Super Rugby tournament in 2016.
'Japan is part of the total global vision of the rugby that we are promoting in the world, especially in the south with Argentina, South Africa, New Zealand, Australia,' Lapasset said. 'That's the top five – with Japan. Not just tier two and tier one, the top five.
'We need to achieve the process that all five will be pushing together to develop the southern competition and to promote the best rugby ever that we can do in the south.
'We did the same in the north with the Six Nations. Now it will be the five nations in the south.'
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