The talented pair are loving the early days of their Japan experience as the global showpiece prepares to begin with the hosts playing Russia on Friday.
Warren Gatland’s side are preparing for their first game with Georgia on September 23 with a training camp in Kitakyushu.
Dragons flanker Wainwright said: “It was a really nice welcome. It was quite crazy and then we got to the hotel where we had a welcome banquet and a bit of a sing song.
“A couple of school kids played bells and the mayor spoke as well. It was really good.”
Ospreys centre Watkin, one of three midfielders in Gatland’s 31-man World Cup squad, added: “It was overwhelming seeing the support we had after landing.
“Hopefully it continues for the rest of the tournament and we can get everyone behind us. Seeing all the banners and the people cheering us was brilliant.
“You see people driving past when you stop at traffic lights and they’ll recognise the three feathers and they start banging the windows and waving. It’s great they’re supporting us so much.”
The Welsh Rugby Union started a World Cup legacy project in Kitakyushu two years ago and the city is covered in Welsh flags and pictures of Gatland’s players. It is a remarkable sight.
Gatland and his 31-man playing squad arrived in the southern Japanese city on Saturday to hundreds of people at the airport. They then took part in a ceremony where Kitakyushu school children sang famous Welsh hymn Calon Lân. Gatland’s players responded with their version of Ar Lan y Môr.
Now as the countdown to the Georgia game begins the focus is entirely on the rugby.
In Kitakyushu Wales are able to walk from their hotel to training and back.
Temperatures are touching 30 degrees with humidity at around 76 per cent and similar conditions are expected all over Japan in the early stages of the World Cup.
Wainwright, 21, now has 12 Wales caps and impressed in the four warm-up matches for Japan.
He said: “It’s been a tough couple of games. We’ve had some good spells and now we’re just looking forward to playing Georgia. It’s a big block of training for us now and we’re focusing on that first game. It’s going to be really important for us.
“There are six of us in the back-row here so competition is very high. If I can get a starting place in the team it would be massive for me.
“That’s what the training camps are there for – to get us in the best possible condition. It’s quite warm here so that will benefit us. We’ve had a couple of days to rest and then we’ll be training in these hot conditions. That will help us massively.
“Since I started playing rugby the biggest goal I would’ve aimed for would be to get selected for the World Cup. To be here and experience the welcome we’ve had with everything that’s gone on has been massive.”
Watkin, who has 16 caps and is only a year older than Wainwright, said: “I want to give myself the best opportunity to try and start for the team.
“If I’m performing well in training and putting pressure on, that will bring the best out of everyone. The better we all train, the better outcome it will be for everyone.
“Regarding training we try to replicate what it’s going to be like in the game with the intensity and how fast it’s going to be. It is tough to get used to and it’s going to take a few days, but with the training we’ve put in over the summer we’re up there with the countries who’ve prepared the most.
“Going to a World Cup is something you aim for as a young player and it’s an honour to be selected and represent your country. Hopefully we can have a successful tournament now.”