or most of the season, the Boston Red Sox have been remarkably solid through the top three spots in their starting rotation. Ace lefty Garret Crochet, comebacking veteran Lucas Giolito and rising homegrown sinkerballer Brayan Bello have a collective 3.28 ERA — which would lead all MLB rotations if the whole Red Sox starting staff were only those three.

Combined, Boston’s top three starters have given the team 450 1/3 innings in 74 starts among them 6.09 innings per start, close to a full inning above the MLB average of 5.21 innings pitched per game by starters.

Unfortunately for the Red Sox, Crochet, Giolito or Bello cannot start every game.

For the fifth spot, Boston has shuffled through 2024 All-Star Tanner Houck, rookie Hunter Dobbins, rookie Richard Fitts, journeyman southpaw Sean Newcomb, and most recently, trade deadline acquisition Dustin May, a former Los Angeles Dodgers hurler.

But the Red Sox have yet to solidify their final rotation spot. For most of the season the Red Sox filled the fourth slot with Walker Buehler, but they released the former Dodgers veteran last Friday after a disappointing campaign.

They appear to be placing they faith in top pitching prospect Payton Tolle to fill the fourth spot.

More MLB: Red Sox Announce Impactful Decision to Shake Up Starting Rotation

That still leaves one gaping hole — a hole that with just 21 games remaining in the season they may not be able to fill.

On Wednesday night against the Cleveland Guardians, manager Alex Cora tried to plug the gap with a “bullpen game,” but the plan blew up in his face when the first three pitchers used, Brennan Bernardino, Jordan Hicks and Steven Matz, combined to cough up six runs in the first two innings, setting up the Red Sox for an eventual 8-1 loss.

To avoid the same problem in next year, the Red Sox could pursue the best pitcher that most MLB fans have never heard of — one who is expected to become available on the free agent market this coming offseason.

That would be Saitama Seibu Lions ace Tatsuya Imai, who is expected to be posted by his Japanese Pacific League club after the season

According to ESPN MLB insider Jeff Passan, the 27-year-old Imai, who has started 155 games in his eight-year NPB career, “is the hardest-throwing starter in Japan, with a fastball that sits at 95 mph and tops out at 99. With a vicious slider, a changeup, a splitter, a curveball and a sinker he picked up this season, Imai has the sort of pitch mix that teams covet.”

Though Imai’s career ERA in Japan is a respectable if not sensational 3.49, the 5-foot-11, 154-pound righty is having a breakout season.

In 143 2/3 innings over 20 starts, Imai boasts a sparkling 1.50 ERA and 0.849 WHIP. The Lions ace has struck out 159 against just 37 walks, surrendering a mere four home runs in 552 batters faced this season.

On June 17, Imai struck out 17 batters in a game against the Yokohama DeNa Baystars, breaking the Lions’ franchise record of 16 set by Daisuke Matsuzaka in 2004.

Matsuzaka went on to pitch six seasons for the Red Sox (and another two for the New York Mets), helping lead Boston to its 2007 World Series championship, then recording an 18-3 record and 2.90 ERA in 2008, his best season in the U.S.

On Tuesday, Imai struck out 10 in a complete-game, two-hit shutout victory over the Tohoku Rakuten Golden Eagles.

According to Passan, “upward of 20 major league scouts” were in attendance at the Tuesday game, so the Red Sox would appear to have substantial competition in bidding for Imai’s services next year.

But as Japanese signings go, Imai should not be in the upper tier — financially anyway.

Passan, citing MLB sources, predicts that the price to acquire Imai will land in the $150 million to $200 million range. Given his relatively youthful age and lack of long-term wear and tear on his arm, that price could be spread over a deal of seven-to-10 years.

In 2024, the Dodgers signed former Orix Buffaloes ace Yoshinobu Yamamoto, who was 25 years old, to a 12-year, $325 million contract.