Retaining Tanaka would be a "compromise" for his Japanese team, since they would receive much less in return for their best player under the new posting system (agreed to earlier this month). With a $20 million cap on posting fees, MLB officials appear to have made the market for imported Japanese players more competitive in America, which could increase the payout for the player, but does less for the teams posting them.
The Japanese teams in the Nippon League, like Rakuten, stand to gain considerably less than they used to under the old posting agreement. Now, a "compromise" -- like retaining Tanaka for another season to maintain his value to the club for another season -- is their best bet at maximizing their end of the deal. It's likely that they accepted these terms in an effort to avoid losing their compensation in the posting process altogether. Had they stood firm and declined to install a cap figure in the agreement, MLB teams could just wait for Japanese players to reach outright fee agency, and their former Japanese clubs would be left out in the cold with nothing gained from their players' departure. Major League Baseball could have also decided to no longer honor NPB contracts, signing away the league's players with no compensation to the teams whatsoever.
While Rakuten will make less than they could have under the old system -- Yahoo! Japan muses that Tanaka's posting fee could have reached a record high of $100 million -- Tanaka stands to become a very rich man if he is posted. Yu Darvish signed a six-year, $60 million pact with the Rangers before 2012, and Tanaka should reach or exceed that figure, especially in this environment with a lower posting fee. That would represent a substantial increase from the more than the 400 million yen he earned with the Eagles last season. That translates to just over $3.8 million US dollars, so Tanaka will likely be looking for a raise if he stays with Rakuten for 2014.
Sources close to Tanaka have said the 25-year old would "absolutely" like to pitch in the majors next season, and looking at the amount of money he could earn, it's easy to see why.