In September, only 8,700 phone numbers were ported (MNP) to AU from other Japanese carriers. That number grew significantly in October, mainly at the expense of Docomo, who lost 74,000 customers via MNP last month - nearly the exact number AU gained through MNP.
Thanks to a little birdy, I confirmed that these are net MNP numbers. The number of customers moving to Softbank decreased in October, but when adding in new contracts, Softbank added the largest number of customers last month.
Docomo is always on the losing end of MNP and likely saw this coming.
Last month they announced a similarly structured Xi (LTE) voice plan as AU and SBM, plus slightly reduced fees for FOMA (3G) data and tethering, the later of which is the main obstacle for using any unlocked handset with Docomo.
Given Docomo's push towards LTE and away from unlimited data plans, I don't expect to see any more changes to the FOMA pricing.