If we base the best pitcher to come from Japan on bWAR alone, then the answer is Yu Darvish.
His resume may be even more impressive than Nomo’s. A four time All Star, Darvish finished second in the 2013 Cy Youn vote, has four seasons with over 200 strikeouts, and his 11.1 K/9 rate is the best mark in major league history of any pitcher with over 1000 innings in their career. Darvish also has 22.1 bWAR, the best mark of any Japanese pitcher.
The statistics certainly speak for themselves. Despite missing time due to Tommy Joh surgery, Darvish has been a relatively solid pitcher. He has posted a 63-53 record, along with a 3.57 ERA and a 1.174 WHiP, striking out 1299 batters with just 384 walks in his 1051 innings.
However, as dominant as Darvish was during his time with the Rangers, he has not been the same pitcher for Chicago. His first season with the Cubs was hampered by injuries, and then he was victimized by the long ball in 2019. At 33 years old, he still has plenty of time to get his career back on track, but all those innings may be starting to wear on Darvish.
Should that be the case, and Yu Darvish is starting to wear down, then Tanaka may be ready to take the crown.