Osuna signed a one-year contract with the Tokyo Yakult Swallows of the NPB on Thursday, Jon Heyman of MLB Network reports.
Osuna was released by the Pirates on Tuesday, Kevin Gorman of TribLive.com reports.
Osuna was designated for assignment Friday.
Osuna went 3-for-4 with a homer, two RBI and two runs scored in Sunday's 8-6 loss to Cleveland.
Osuna went 2-for-4 with a solo home run and a double in Saturday's 8-0 win over Cleveland.
Osuna is not in Thursday's lineup against the Cubs.
Osuna will start in left field and will bat seventh Sunday against the Cardinals.
Osuna was recalled by the Pirates on Thursday.
Osuna was optioned to the Pirates' alternate training site Wednesday.
Osuna will make a rare start in left field and bat fifth against Cleveland on Thursday.