Samoa have beaten the Brave Blossoms in 11 of their 15 previous matchups but haven't tasted success since 2012.
The Manu were thumped 34-0 by Scotland in their previous match but flanker Chris Vui said there is still a lot of belief in the squad.
"After that Scotland game we still have belief in what we're trying to do - Japan's in our way and it's just another team we've got to get past to make those playoff games - and there's huge belief in this squad," Chris Vui said.
Samoa have made six changes to their starting fifteen for tonight's clash in Toyota City, with prop Jordan Lay, hooker Seilala Lam, lock Piula Faasalele and first five UJ Seuteni making their first starts of the tournament, while Dwayne Polataivao returns at halfback.
Ed Fidow retains his place on the left wing after his red card against Scotland received no further punishment while Ah See Tuala starts on the right wing in the oafter missing the opening two games through injury.
A bonus point win could see Samoa climb as high as second in Pool A and assistant coach Alistair Rogers said they're excited by the opportunity in front of them.
"We know as a team the threats that Japan pose: they've got a good tight-five, the back-row is strong, good backs. Obviously the boys (in our team that play in Japan) can share a little bit of that experience but we certainly are aware of what's coming so it's really about our game and getting ourselves prepared as best we can for that challenge," Alistair Rogers said.
Samoa's Prime Minister Tuilaepa Sailele Malielegaoi, who is also chair of the country's rugby union, visited the players in the camp on Thursday and Chris Vui said the players appreciate the support.
"He's a funny old character, Mr Prime Minister Tuilaepa. It was good having him in yesterday - he spoke to us with a full heart and he said some funny jokes, just to keep the mood nice and chill, so it was good having him in yesterday and he was just giving us some words of encouragement leading into Japan so yeah he's a good fella," Chris Vui said.