For Tatsuya Imai, the best Japanese free agent pitcher this offseasontime is running out.
The 27-year-old right-hander must sign with an MLB team before his posting window expires at 5 p.m. ET on Friday. Although few teams have been definitively linked to the longtime Seibu Lions pitcher, the overwhelming expectation within the industry is that Imai will come to terms with a big league club before the deadline.
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That’s because he offers an attractive combination of ceiling and floor at a relatively young age for a free agent pitcher.
To be clear: Yoshinobu Yamamoto, he is not. Imai’s athleticism, track record and fielding quality pale in comparison to that of the 2025 World Series MVP. As such, Imai won’t sniff at the 12-year, $325 million deal Yamamoto made two winters ago. However, a substantial salary is required; Imai is expected to eclipse the $100 million mark. At least that’s what his representative, agent Scott Boras, is aiming for.
And based on Imai’s talent and resume, that’s a very reasonable goal.
Across the Pacific, Imai is a household name, a famous figure for some time. He rose to fame during the 2016 Summer Koshien, the hugely popular Japanese high school baseball tournament. In the finals, Imai delivered a heroic performance as high school ace Sakushin Gakuin, pitching a complete game of nine strikeouts and one run. This propelled him to national prominence and the top pick in the 2016 NPB draft.
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Professional success did not come immediately. As a 20-year-old rookie with Seibu in 2018, Imai struggled to a 4.81 ERA in 78 2/3 innings. Things gradually improved as he became more familiar with the top level, but injuries and lack of control limited his production.
The free passes, in particular, were a huge bugaboo. Between 2018 and 2023, Imai posted a total walk rate above 13%. For comparison, only one MLB starter in the last decade (Blake Snell in 2023) has had such a wild season. Last season, only two qualified starters (Cleveland’s Gavin Williams and Anaheim’s Jose Soriano) had walk rates above 10 percent. Simply put, it was an unsustainable lifestyle for Imai.
So the 5-foot-11 right-hander changed course, deliberately changing his mechanics to improve his strike throws. In turn, his numbers took a huge step forward, with the walk rate dropping to 9.8% in 2024, then 7% in 2025. Even more impressive, Imai’s strikeout numbers increased along with his strengthening of control.
It all culminated in a phenomenal 2025 season in which Imai achieved a 1.92 ERA with more than one strikeout per inning over 24 starts.
This breakthrough has Imai zooming in on MLB wish lists, as virtually every club — except, perhaps, the Dodgers — could use another rotation piece. And unlike his fellow Japanese free agent Munetaka Murakami, whose high-risk profile has hampered his marketImai seems like a reliable proposition.
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Some of this is simply a product of the hitter/pitcher division when it comes to NPB players. Predicting whether or not a Japanese hitter will adapt to MLB pitching is a much trickier exercise than doing the same thing with a Japanese pitcher. Advances in tracking data mean we can compare Imai’s arsenal, trigger points, speeds and pitch shapes to those already present in the bigs. This gives us – and, more importantly, MLB teams – a better idea of how arms will move from the second best league to the best league in the world.
And Imai’s stuff passes the smell test. Last year, his heater averaged about 95 mph, above the MLB starter average of 94.1. He relies heavily on that four-seam fastball, especially against right-handed hitters, to whom he threw the pitch 53 percent of the time. His slider accounted for an additional 39 percent against same-side bats, meaning Imai rarely uses a third pitch against righties. That puts him in a small group of pitchers — think Spencer Strider, Jacob deGrom, Jared Jones — with such a small right-to-right mix.
Against southpaws, Imai turns to his changeup and splitter to keep his opponents off balance, using those to deliver 16% and 7% of the time, respectively. It all comes out of a relatively low location, which adds deception to its heater/slider combo.
The indomitable Yuri Karasawa of JapanBallthe Internet’s premier source for coverage of Japanese baseball in English, compared Imai to Mariners right-hander Luis Castillo in a recent article. YouTube video. This is an interesting lineup, based on their similar heater/slider reliance and low arm slots.
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One key difference: Castillo has been remarkably durable for most of his career, while Imai has never started more than 25 games per season. But if Imai can match Castillo in terms of efficiency, it would be a massive win for the team that ends up with the Japanese pitcher. No favorite has emerged yet, as the typical multitude of deep-pocketed clubs in Los Angeles, New York and Toronto have fairly stocked starting lineups.
The Mets, whose pitching woes sank their 2025 season, have been linked to Imai, but they would likely need to subtract from their assortment of weapons if they brought him back. The Phillies, potentially without ace Zack Wheeler for the start of the season and about $35 million less than last year’s final payroll, would make sense. The Cubs desperately need another frontline arm, but have not shown the willingness to increase their payroll much beyond $200 million. The same goes for the Giants, who have yet to add much to their major league roster this winter.
To be fair, a player of Imai’s caliber fits just about anywhere; Playoff hopefuls in Baltimore, Detroit, Miami, Arizona and even Sacramento should all pick up the phone and inquire. His history of incremental improvement year over year, willingness to make adjustments, athleticism on the field, and arsenal suggest he will be a solid mid-rotation pitcher in MLB, with the potential to do more if he continues to develop.
He’s a pretty exciting player, who should be a lot richer in a few days.
