In September, Tanaka notched his 21st straight win to break Japan's previous record of 20 in one season set by Kazuhisa Inao in 1957.
Going back to Aug. 19, 2012, the last time he lost a game, Tanaka has won 30 games in a row, including two wins in the playoffs this year.
All the success this season has raised Tanaka's profile among teams in Major League Baseball, making him the most sought-after Japanese import since Yu Darvish.
According to media reports, at least seven major league teams, including the New York Yankees and Boston Red Sox, are expected to enter the Tanaka sweepstakes once the season ends.
Tanaka isn't eligible for free agency but it's expected he will be made available via the posting system that allows MLB teams to bid for the negotiating rights to Japanese players.
Darvish, Daisuke Matsuzaka and Ichiro Suzuki all went to the majors under the same system.
A first-round draft pick for the Eagles in 2006, the 188-centimeter (6-foot-2), 93-kilogram (205-pound) Tanaka is a right-handed power pitcher with a high three-quarters delivery.
With a fastball in the mid-90's, Tanaka has impressed major league scouts. He also throws a splitter with downward movement, a slider and the occasional curveball.
Like Darvish and Matsuzaka, Tanaka was a standout at Japan's high school baseball tournament. He struck out 459 batters over three seasons, surpassing Matsuzaka's mark of 423.
In addition to Tanaka, the Eagles will be counting on two former major leaguers in the Japan Series.
Former Yankees outfielder Andruw Jones batted .243 with 26 home runs and 94 RBIs in 143 games to help the team to its first Pacific League pennant.
Also making a major contribution is former major league infielder Casey McGehee, who batted .292 with 28 home runs and 93 RBIs.