The Boston Red Sox have been searching for an ace all offseason. They were connected to left-handed ace Blake Snell before Snell signed a massive five-year deal with the Los Angeles Dodgers. Boston is also connected to pitchers like Jack Flaherty, Corbin Burnes, Max Fried and other top free agent arms. Besides free agents, Boston is rumored to be in on top trade candidates like Sonny Gray or Garrett Crochet.

The most likely scenario finds Boston adding two starters this winter. One from the list of pitchers above and one unexpected mystery arm.

The unexpected arm could very well come from the Seattle Mariners, who have a plethora of talented pitchers with a lackluster lineup. If the Mariners look to move a pitcher, Luis Castillo would undoubtedly be the most sought-after.

This blockbuster Red Sox-Mariners trade would solve Boston’s biggest problem

Castillo is under contract through 2027 with a vesting option in 2028. His contract is decent in size, so Seattle would likely need to pay a little bit of the deal to move Castillo. Boston would be one team that could bite on that idea.

In this deal, the Mariners should be assumed to be paying about a third of Castillo’s remaining contract. Because of that, Seattle would land quite a loaded return.

Wilyer Abreu is somebody Boston has been rumored to want to move this winter. Abreu, 25, posted a 3.5 WAR while slashing .253/.322/.459 and earning a Gold Glove in the outfield. He’s an incredibly valuable asset for Boston, so shipping him to Seattle would be a tough move to make. With the Mariners talented outfield, they’re not in the market for an everyday outfielder, but Abreu is too talented to pass up on.

Meidroth, 23, slashed .293/.437/.400 at the Triple-A level in 2024. He has an innate ability to reach base while hitting nearly .300. The Mariners need infielders and Meidroth is an MLB-ready infielder that could make a difference as soon as this season.

Garcia, 21, slashed .286/.356/.536 as he flew up the ranks of the minor leagues last season. He’s a serious power threat with a growing ability to put the ball in play and reach base.

Castillo has been a Bonafide ace for quite some time now. Over the last five seasons, he’s been among the best pitchers in the league, consistently posting ERAs below 4.00. He would be a huge addition to the Red Sox rotation, especially if Boston can add an arm like Max Fried alongside him at the top of the staff.