5 things to know about rumored Red Sox target and Japanese pitcher Tatsuya Imai

Boston Red Sox

Imai has been one of the top pitchers in Japan over the last couple of years.

By Conor Roche

December 20, 2025 | 4:40 PM

3 minutes to read

The Red Sox seem to be in the mix for another notable free agent.

Boston has been connected to Japanese right-handed pitcher Tatsuya Imai and is believed to be one of the clubs most interested in the pitcher, MLB.com’s Mark Feinsand recently reported.

Imai, 27, has pitched for NPB’s Saitama Seibu Lions in Japan since 2017. Here are five things to know about the rumored Red Sox target.

He’s emerged as one of NPB’s best pitchers, breaking records once held by Daisuke Matsuzaka.

Imai has quickly emerged as a top arm in NPB over the last couple of years. He’s been named an All-Star in each of the last two seasons, posting a 1.92 ERA over 24 outings in 2025 after logging a 2.34 ERA in 25 outings in 2024.

In terms of strikeouts, hits, and walks, Imai has logged very similar strikeout rates over the last two years (9.7 and 9.8 per nine innings in each of the last two years). He had a 0.892 WHIP in 2025 after recording a 1.165 WHIP in 2024. Imai did have some control issues prior to his recent surgence, with a walks per nine rate over four in every season before the last two years.

Imai has averaged roughly 6 2/3 innings pitched per outing over the last two years, so he’s proven he can pitch deep into games. That helped him set a Seibu Lions record this past season, when he struck out 17 hitters in one game. That record was previously held by former Red Sox pitcher Daisuke Matsuzaka. He also pitched a combined no-hitter this year.

He’s projected to be a middle-of-the-rotation arm.

The toughest thing about signing international free agents is projecting how their game will translate to MLB. The Red Sox have had mixed success in the past in signing high-profile international free agents, with Matsuzaka displaying some high-end stuff before cooling off in his tenure in Boston. More recently, Masataka Yoshida has been able to hit for average, but has left a lot to be desired elsewhere with his game.

For Imai, the expectations don’t seem to be superbly high, at least compared to Yoshinobu Yamamoto when the Dodgers signed him two offseasons ago. ESPN’s Kiley McDaniel believes Imai would ideally be a No. 3 starter for an MLB team, believing his ERA would sit in the 3.00-4.00 range. MLB.com’s David Adler noted that Imai’s ceiling isn’t as high as Yamamoto’s, either.

His fastball is his primary pitch, but his slider has been his most effective.

Imai’s fastball has become a pretty productive pitch for him. His average fastball sits around 95 mph, but tops out at 99 mph. He generated a 20 percent whiff rate with the pitch in 2025, throwing a fastball in 48 percent of his pitches, per MLB.com. For reference, that number is better than the whiff rate Lucas Giolito and Brayan Bello were able to produce for the Red Sox last season.

Imai’s slider, meanwhile, generated a 46 percent whiff rate as he used the pitch 33 percent of the time in 2025, per MLB.com. Only three pitchers generated a higher whiff rate with their slider last season. Among qualified pitchers, only seven MLB pitchers had a higher whiff rate with their slider last season.

Imai also has a splitter, changeup, and curveball as part of his pitching arsenal.

Which pitchers has he been compared to?

Imai has a smaller frame, standing at 5-foot-11, but both ESPN’s Kiley McDaniel and MLB.com’s David Adler compared him to 6-4 Blue Jays pitcher Trey Yesavage. Adler made the comparison because he thinks that Imai’s slider has a similar “backwards” movement as Yesavage’s, while McDaniel made the comparison due to having a similar approach in their attack.

Adler also compared parts of Imai’s game to Mariners pitcher Luis Castillo, Blue Jays pitcher Max Scherzer, and Pirates ace Paul Skenes. On top of that, he thinks Imai’s fastball is similar to another pitcher the Red Sox have recently targeted, Joe Ryan, based on their similar low arm slot.

He has until Jan. 2 to sign with a team. Who has been linked to him?

Unlike most other free agents, Imai has to go through a complex process. He was posted by his NPB team in November, meaning he only has a 45-day window to sign with a team. Whichever team signs Imai will also have to pay a posting fee, which could go well into eight figures.

The Yankees have been the team most linked to Imai this offseason. However, Yankees manager Aaron Boone said on Friday that the team has yet to meet with Imai. The Cubs are also reportedly in the mix for Imai.

The Athletic projected that Imai would receive an eight-year, $190 million contract at the start of the offseason.