Williams has long been a target for a number of Japanese sides yet the 35-year-old confirmed his decision to call time on his stellar career after playing for the Barbarians against Wales just over a week ago.
Now, though, the former IRB World Player of the Year is expected to sign for Mitsubishi Dynaboars in Division Two of the Japanese League.
Williams is reportedly keen on a one-year deal with the Sagamihara-based side despite his role as an ambassador at the Ospreys where he spent eight seasons since their inception in 2003.
A double Grand Slam winner with Wales in 2005 and 2008, Williams scored 58 tries in 87 internationals for his country.
He bagged two more for the Lions in his final game in the famous red jersey as Britain and Ireland's elite beat the Springboks in the third Test in Johannesburg in 2009.
And after ending his Wales career in fine style with a try against Australia with his last touch of the ball back in December, Williams enjoyed an even more remarkable ending to his time in club rugby as he crossed for a brace of tries in the 2012 RaboDirect PRO12 Grand Final.
The second of those tries came with just two minutes remaining of his club career, setting up Dan Biggar's tournament-winning conversion against Leinster at the RDS.
Japan has seen a whole host of foreign stars grace its game in recent years, with the likes of Wallaby legend George Smith and South African star Fourie du Preez featuring in last season's Top League Final.
England flanker James Haskell played for the Ricoh Black Rams after the 2011 World Cup, while Williams' 2009 Lions team-mate Riki Flutey will be in Japan next season.