In the Early Samurai Japanese (3/55) list, before 1020 all Ax, Ps, Bw, and Bd are compulsorily regraded to Irr Bw (O) unless double-based behind cavalry.
As written, this applies not only to the "normal" infantry in the list, but also to the ladies and boys guarding baggage and to Sohei allies. Acc'd to Duncan, it probably shouldn't apply to the former, and the later shouldn't be available before 1020 in the first place.