Miyagi Prefecture announced today that they are looking for a new sponsor to purchase the naming rights to Miyagi Stadium. Nippon Seishi's contract with the Prefecture and the Rakuten Eagles is set to expire this year.
According to the announcement, the prefecture is looking to sign a three-year deal that begins on January 1, 2014 and is worth at least 200 million yen a year. Bids will be accepted between November 5 and December 4. Additional terms and conditions can be found at the official announcement link below.
Source: official announcement
[UPDATE 12/4 @ 10:59pm]
The media learned today that two companies submitted bids. An announcement will likely be made later this month after Miyagi Prefecture and the Rakuten Eagles have had a chance to discuss the offers.
Source: Sponichi 12/4/2013