Saitama Seibu Lions right-hander Tatsuya Imai hurled his second consecutive complete game shutout last Tuesday, holding the Tohoku Rakuten Eagles to just two hits. He struck out 10 batters and needed only 100 pitches, just one shy of a Maddux.
The 27-year-old has made dominant outings like this a regular occurrence in 2025. He owns a 1.50 ERA (196 ERA+) through 20 starts, with the most recent outing marking his fifth complete game and third shutout of the year, which includes a franchise-record 17-strikeout masterpiece against the Yokohama DeNA BayStars on June 17.
Apart from a rough patch in July, when he posted a 5.40 ERA, Imai has unquestionably been among the top two or three starters in Nippon Professional Baseball this season. His 1.50 ERA marks a clear leap from the 2.34 ERA he posted between 2022 and 2024, and his peripherals are even more impressive. His 6.7% walk rate is well below his career average of 11.6%, and he tops all qualified pitchers in FIP- (61), strikeout-minus-walk rate (22.1%) and swinging strike rate (15.9%).
The Tochigi, Japan-native has long built his reputation on a power fastball-slider combo, slicing through right-handed hitters year after year. Lefties, however, remained his trouble spot, with a 13% dip in strikeout-minus-walk rate and a .686 OPS allowed compared to .487 for righties in 2024. But this season tells a different story: lefties are managing only a .505 OPS, while righties have been held to an even stingier .425.
A look at where Tatsuya Imai ranks percentile-wise in NPB as of Sept. 10, 2025. (Yuri Karasawa/Yakyu Cosmopolitan)
His approach to righties has stayed steady, with 92% of his pitches coming as fastballs or sliders. The four-seamer averages 95 mph, but he’ll dial it down to 91-93 in low-leverage spots and reach back for 97-99 with runners in scoring position. His slider, sitting in the mid-80s, features tight movement and tunnels well with the heater. Against lefties, though, that fastball-slider share drops to 73%, with the rest of his arsenal consisting of changeups, splitters, and curveballs.
In his latest outing, Imai also unveiled a new weapon: a sinker he learned from teammate Ryota Itogawa. He threw it 19 times, primarily to opposite-hand hitters, further diversifying his mix. Despite the name, the pitch comes in at 82-85 mph with a grip that resembles more of a vulcan changeup.
This season’s strides in his platoon splits and overall command have left many fans asking the same question: is Imai bound for Major League Baseball? The biggest factor outside of Imai’s control is whether the Seibu Lions agree to post him this offseason. With teammate Kona Takahashi already expected to be posted, the club may be reluctant to part with two rotation anchors at once. Still, Imai will reach domestic free agency next year and international free agency three years from now. If the Lions hold on too long, they risk losing him for nothing rather than collecting a sizable posting fee this winter.
Assuming he’s posted after the 2025 or 2026 season, the focus shifts to how his stuff will translate. In MLB, Imai won’t have the luxury of easing off against the bottom of the order as he’ll be asked to sustain higher velocity across a full season. His fastball carries a 26.9% called strike plus whiff rate this season, underwhelming for the velocity, as the shape itself isn’t particularly elite.
Still, he consistently locates it at the top of the zone and generates swings and misses on it, a trait that could make adapting to MLB easier. How his slider fares in MLB will be another determinant of his success. Its tighter movement profile (a conscious design choice he made after 2023) gives it a unique look, though teams may prefer if he adds more sweep or depth.
Ultimately, Imai’s ceiling is comparable to Kodai Senga as a strong 2 or 3 in the rotation, though his floor is a bit lower since his slider, despite elite results in NPB, lacks the world-class outlier status of Senga’s ghost fork. However, Imai brings a much cleaner health record than Senga and will arrive in MLB two or three years younger, giving him a longer runway for success and likely earning him a bigger payday.
Photo: Tatsuya Imai of the Saitama Seibu Lions is one of the top pitchers in Nippon Professional Baseball.
