Naoyuki Umasawa was the lesser-known hurler from Japan that few outside the United States have ever heard of. He wasn't as popular as Yamamoto or Imanaga. He was just sidelined. He was signed by the Rays in January but missed the 40-man roster. He was then traded to the Boston Red Sox where he played in its AAA system with a 4.80 ERA (earned run average) until being called up to the Major League level. In the NPB, the domestic league in Japan, he played for one team, The Nippon Ham Fighters, the same team Shohei Ohtani played for, where he boasted a 3.19 ERA over his 9 year career.
Unlike his fellow countrymen, Naoyuki doesn't have those so-called electric characteristics. He has a 90 mph fastball. But, what he does have, is a mixed bag of pitches which he utilizes well, especially his splitter, slider, and curveball. He seems to have good control of the strike zone.
In the NPB, he wasn't known to be a strikeout pitcher, striking out only about 17% of the hitters he faced per nine innings. In 15 innings in Triple-A, he struck out 26% of hitters. Although it's a small sample, Naoyuki did finish his NPB career in stellar fashion, boasting an ERA of 2.96 at the end of the 2023 season, striking out 124 batters in 24 games, indicating he has potential to perform well throughout an entire season.
Alex Cora, the skipper for the Red Sox, sees potential in Naoyuki. He encourages him to use more of his splitter, which is easily the 30-year-old's best pitch. Though his fastball is only around 90 mph, it is deceptive, as it is often difficult to determine where it will eventually land, causing hitters to believe the ball might be some other pitch.
It is still difficult to know how good he will be at the big league level, but if he uses that splitter and mixes it with his deceptive fastball, he will do just fine. The best comparison for Naoyuki would be Shintaro Fujinami, who is his complete opposite. Unlike Fujinami, his fastball can't pass over 100 mph and unlike him, he has good command of the strike zone.