Mariners finally have reason to be nervous about Astros after Tatsuya Imai signing

If the 2025-26 MLB offseason had ended on Wednesday, the Seattle Mariners could have counted themselves as one of the biggest winners of it. Sure, they lost Jorge Polanco, but they retained Josh Naylor and added Rob Refnsyder, Jose. A Ferrer and Andrew Knizner.

Meanwhile, no other team in the AL West had really put itself in a position to rebel against the Mariners' status as the division's defending champs. Really the only two teams that could have done so were the two Texas clubs, and both seemed more "stuck" than "aggressive."

Yet it seems that the arrival of 2026 on Thursday jolted some life into the Astros. They now have Tatsuya Imai in their starting rotation, and it's hard to read that as anything other than bad news for the Mariners.

Mariners finally have reason to be nervous about Astros after Tatsuya Imai signing

The Astros didn't seem like a favorite for the 27-year-old Imai when his posting window opened in November, but his market clearly did not push him toward the $150 million contract that was predicted by MLB Trade Rumors. He's with Houston on a three-year deal that guarantees about a third of that at $54 million.

As noted by ESPN's Buster Olney, this happened in part because Imai ended up playing to a mostly chilly audience in making his pitch. Faced with going back to Japan or betting on himself, he understandably chose the latter.

Imai had sub-3.00 ERAs in 2022, 2023 and 2024 while pitching for the Seibu Lions, and he got his ERA down even further to 1.92 last year. So if it's a question of what MLB teams are worried about, his size (5-foot-111, 154 pounds) and tendency to walk guys are two potential culprits.

The stuff, however, seems legit. Imai can get his fastball up to 99 mph, and it's just one of five pitches in his arsenal. And in the opinion of Ben Clemens of FanGraphs: "He may be a tweak away from having better stuff than his already solid five-pitch mix."

If you're the Mariners, this is the part that scares you. The Astros have been a mainstay near the top of the AL West precisely because they know how to maximize stuff. No team has as many strikeouts as they do since 2015, and that comes with the lowest overall contact rate in the league as well. One of their best recent success stories was Yusei Kikuchi, one of Imai's countrymen, in 2024.

The Mariners still project as the better team in 2026, but we're talking a difference of 45.0 WAR to 42.1 WAR. That's a little close for comfort, and it doesn't even count a projection for Imai yet. If he forms a dynamic duo with Hunter Brown hot off his turn as an AL Cy Young finalist, the Mariners' odds of repeating as AL West champs will be that much more complicated.

Then again, Seattle has every right to have a "Bring it on" mindset. Beating Houston was a key part of their ascension in the AL West in 2025, so they can look at the Astros' deal with Imai for what it is: them trying to play catch-up.