The media learned on Monday that Koji Akiyama is planning to step down after the season. Akiyama has already informed the Softbank Hawks of his intention to resign. The organization has been trying to get him to change his mind, but the pressure to do well after multiple high-profile free agent signings and the team's slow down at the end of the season may have wore him down. Family and health issues may have also factored into the decision.
A press conference is scheduled for later today.
[UPDATE @ 10:06pm]
The Hawks formally announced that Akiyama will be stepping down after the season. They also posted footage from the press conference at Ustream.
Source: official announcement
[UPDATE 10/16 @ 1:57am]
Akiyama's wife fell sick three years ago. His wife's health factored into his decision not to manage at the 2013 World Baseball Classic and was likely one of the reasons why he decided to step down as manager of the Hawks. His daughter heading off to college this year also probably played a part.