NHK reports on the matter
The yen has strengthened on the headline here with USD/JPY falling from 106.70 to a session low of 106.21 as the Nikkei takes a tumble, falling by over 1% now.
NHK reports that Abe is planning to resign due to health reasons and wants to avoid disruptions to the government due to his illness. This goes against prior reports that he is expected to carry on with his incumbent position until next year.