Manu announced last week 2024 would be his last in the NRL with the Sydney Roosters before moving to Japan and joining Toyota Verblitz.
The 27-year-old has won 17 caps for the Kiwis but if all goes well in Japan it could be a springboard to him one day representing the All Blacks.
New Zealand Rugby has strictly pursued a policy of only calling up players plying their trade domestically and Manu would likely have to return to New Zealand if he wanted a shot at selection for the 2027 World Cup.
History is also stacked against the Roosters centre due to the fact, since rugby union became openly professional in 1995, only Roger Tuivasa-Sheck and Williams have won caps for New Zealand in both codes.
Working in Manu's favour, however, is the fact Steve Hansen, who helped guide Williams' union career, is the director of rugby at Toyota Verblitz with Ian Foster installed as coach next year.
But, speaking for the first time since finalising his switch, Manu is keen to downplay his prospects of international honours, stressing the most important goal was learning a game he hadn't played since his school days.
"If I'm playing good then yeah (I'd love an All Blacks jersey), but that's not the main focus, I've got to learn the game," Manu told AAP.
"I'm really happy that those two coaches are there along with Aaron Smith so I want to build off that.
"It was a personal decision and I obviously had to look for the best option.
"I felt that was what was best, talking to the coaches there, I just want to go over there and learn and develop as a rugby player."
Manu has yet to begin learning Japanese and said he had agonised over leaving the club and the tutelage of Trent Robinson, who has been a constant in his NRL career.
"It was a tough decision, I had a lot of chats with 'Robbo' and how long I've been here … I came over here when I was 16, it's a long while and it's the only thing I've known," Manu said.
"This place, the club, as well, I made the decision and I'm content with it and I've just got to enjoy every moment and make the most of my last year."
Manu has two NRL premierships to his name but if the Roosters can snap their inconsistent performances he hopes to be able to add a third.
A 4-4 record perhaps belies the quality in Robinson's star-studded side and Manu knows the Roosters have it within themselves to start upping the ante.
"We're sort of up and down and we haven't really proven too much," Manu added. "We've got to find that consistency, that week to week is the challenge for us.
"We've got to stay with that and then hopefully we can start racking up a few games in a row."
