The 27-year old was deemed surplus to requirements after a year which saw the primarily left-winger score just one goal in the Bundesliga from 25 appearances.
Despite bad scoring form for club, Okazaki has fine form for country where he has scored 34 goals in 65 appearances including 2 at the confederations cup.
Okakazi joins Mainz for an undisclosed figure which will probably be revealed in due course.