I have a feeling that his name will come up a lot this offseason, but not be tied with the Reds. Here is some information on him:

http://www.nytimes.com/2013/10/24/sp....html?hpw&_r=0

So far, nothing has been able to disrupt Tanaka, who finished the regular season 24-0 with a 1.27 earned run average and a save, then was 1-0 with a shutout and a save in the playoffs after Rakuten won its first Pacific League title. In the regular season he faced 822 batters and gave up only 6 home runs. Incredibly, his performance came in a season marked by a juiced ball controversy: Wladimir Balentien of the Tokyo Yakult Swallows hit 60 home runs to shatter Sadaharu Oh’s cherished record of 55 homers, set in 1964.
One veteran scout in Japan, who asked not to be identified because he was not permitted to speak publicly about players, said Tanaka’s fastball ranges from 90 to 97 miles per hour and his splitter and slider are exceptional, both to left-handed and right-handed batters.

The scout noted that Tanaka, who turns 25 Nov. 1, has the ability, like so many of the best pitchers in baseball, to “dial it up” in critical situations. The fastball gets a little extra jump and the split-finger fastball additional bite.

The command on his curveball and changeup are average, he said, and Tanaka faced the ace of the opposing team only four times this season. But who is quibbling?

“He won’t go 24-0 in M.L.B.,” another player evaluator said. “But he is a talent.”
Tanaka is expected to be the focus of an intense bidding war. Teams like the Yankees, the Red Sox, the Blue Jays, the Mariners, the Dodgers, the Rangers and the Angels are expected to submit a posting bid with the hope of then negotiating a multiyear contract with him, perhaps exceeding the six-year, $56 million deal that Yu Darvish received two years ago.

The old posting system, in which the player can negotiate only with the highest-bidding team, is in the process of being restructured to give the player more choices about which team he can play for. So far, Tanaka has not declared that he will ask to be posted after the Nippon Series, Japan’s version of Major League Baseball’s World Series, but many expect him to.
Career Stats:
http://bis.npb.or.jp/eng/players/11215114.html
http://www.baseball-reference.com/ja...d=tanaka003mas

Interesting, extensive scouting report here:
http://irfast.blogspot.com/2013/08/m...ng-report.html

I do want to be clear: these statistical comparisons are the only real similarities between Tanaka and Darvish. Other than that, they are both righties that pitched in Japan that have sliders that they throw a lot. Everything else is different, from body type, mechanics, fastball velocity, pitch selection, etc. Darvish is not a valid comp to Tanaka, other than the fact that they were both really really good in the same league.
The easiest comp for Tanaka in the Majors is Hiroki Kuroda since they have somewhat similar fastballs, and rely a lot on splits (assuming you call Tanaka's "forkball" a split) and sliders. Obviously they are at totally different moments in their careers (though Kuroda is pitching as effectively, if not more effectively, than he even has), and Kuroda was throwing quite a bit harder at Tanaka's age (he was averaging over 92 MPH in 2008 with the Dodgers at age 33). Iwakuma also seems lazy and racial, but we have to recognize that the pitching style in Japan differs from the pitching style in America, which causes comps that may seem lazy and racial when looking at pitch selection. There aren't many American pitchers who use splitters at all, much less have it as an out pitch. That is why Dan Haren is an interesting American comp, especially Dan Haren's 2009. Haren's slider was a MPH harder, but the fastball and splitter were about the same as Tanaka. It is noteworthy that 2008-2010 Haren was better than Kuroda has been in America (at least by fWAR).