Iwakuma had previously announced at the tail end of the 2018 campaign that he’d return to his native country to keep pitching. The 37-year-old had made one last effort to return to the majors last year, but ended up making only a pair of minor-league appearances with the Mariners — the only MLB organization with which he has pitched.
The Seattle organization got plenty of value from Iwakuma over the years, enjoying 883 2/3 total innings of 3.42 ERA ball spread over six seasons. He was a strong contributor over most of that span, though more recently shoulder problems arose that kept him off of the mound.
Iwakuma will return to a league in which he long thrived before coming to the majors. Over 11 campaigns with the Osaka Kintetsu Buffaloes and Tohoku Rakuten Golden Eagles, Iwakuma worked to a 3.25 ERA with 6.9 K/9 and 2.0 BB/9. He wrapped up his first stint in Nippon Professional Baseball in 2011, launching his MLB career in the ensuing season.