"I just want to experience the culture, and get to understand it and embrace it," Williams told ONE Sport.
"It will take me a while to break the language barrier, but hopefully in the next month or two, I can do that."
The Wild Knights play the Black Rams, fellow All Black Ma'a Nonu's former team, to kick off their season.
Williams, who is also New Zealand Professional Boxing Association heavyweight champion, will be based in Ota, an hour's drive outside Tokyo.
The 27-year-old centre played the last of his 19 Test matches, for the time being at least, in the All Blacks' 22-0 win over Australia at the weekend.
New Zealand's selection policy is to not pick players competing overseas to represent the world champions.
Williams instead will now focus on the Japanese Top League season and is expected to return to rugby league in Australia next year.
His Wild Knights club stormed to the Japanese title undefeated in 2007/2008 but in recent years have ceded supremacy.
Japan hosts the Rugby World Cup in 2019.