London - Luke Charteris believes Wales will face a much-improved Japan side when they take on the Cherry Blossoms at the Principality Stadium on Saturday.
It will be Japan's first match in Cardiff since 2007 and sees them back in Britain following their shock upset win over rugby heavyweights South Africa at last year's World Cup.
The Japanese, who started their tour of Europe with a 28-22 win over Georgia in Tbilisi on Saturday, also beat Wales 23-8 the last time the teams met in Tokyo three years ago although the Welsh were without several first-choice players due to the 2013 British and Irish Lions tour of Australia.
"You have got to say they (Japan) have gone on again from two or three years ago," said Wales lock Charteris on Wednesday.
"The boys know the challenge that awaits - it will be a tough game again.
"As a squad, we watched their victory over South Africa in the team room, cheering them on.
"The beauty of the World Cup is that you face teams you do not meet very often.
"Probably Scotland were quite lucky to get Japan on a short turnaround (at the World Cup), otherwise that game would have been more interesting."
Japan are now being coached by former New Zealand international Jamie Joseph and Charteris said: "We know it will be tough on Saturday, even though they have changed since the World Cup with a new coaching team and the next generation of players.
"They like to play a high-tempo game and will be different to sides we are used to facing.
"Japan, Romania, Georgia - these are the teams who are as a whole certainly closing the gap between tier two and tier one nations. It is definitely getting a lot smaller."