 On December 3, 2018, Seibu announced it was allowing Kikuchi to enter the posting system to play in Major League Baseball (MLB), with the 30-day period starting a month later.On January 2, 2019, Kikuchi signed a four-year contract with the Seattle Mariners.Kikuchi made his MLB debut on March 21, 2019, going 4.2 innings while allowing 2 runs (1 earned) and striking out 3.