The world's biggest retailer, Wal-Mart Stores Inc, is making its first foray into the tough Japanese market by taking a 6.1 per cent stake in the country's fifth-largest supermarket chain Seiyu Ltd. US-based Wal-mart will pay around $46 million for the stake, with an option to raise its share to 33.4 per cent by the end of this year, 50.1 per cent by the end of 2005 and 66.7 per cent by the end of 2007. The total equity injection would be 260 billion yen, or $2 billion.