Tanaka, currently playing for the Tohuku Rakuten Golden Eagles, has a 1.20 ERA over 22 starts. The 24-year-old is in his seventh season for the Golden Eagles and holds a career 2.32 ERA and 1.11 WHIP.
Darvish was more acclaimed than Tanaka when he came to the United States, but the two pitchers have posted similar strikeout and walk numbers in the Japan Pacific League. Though Tanaka reportedly has good secondary pitches, his fastball is not overpowering like Darvish's.
The Rangers paid over $100 million overall to acquire Darvish's services. They won the posting auction with a bid of nearly $52 million, then signed Darvish to a six-year deal worth $56 million. Darvish has proven to be one of the best pitchers in the MLB with a 2.91 ERA and a league-leading 240 strikeouts in just 180 innings this season.
Darvish is expected to lead the Rangers starting staff in 2014, alongside Derek Holland and Martin Perez. Matt Harrison, who underwent back surgery earlier in 2013, is also expected to be at full strength and in the rotation. Though Matt Garza is a free agent at the end of the season and may not be re-signed, the Rangers have Alexi Ogando, Nick Tepesch, and Neftali Feliz, all of whom could grab the fifth starter role next year.