Actually, I wonder if maybe he's defeating Muramasa as a means to ensure he controls him...kinda like Ichigo had to do to get his Bankai, and like they all have to do to regain control of their zampakuto's.

I think the woman was Byakuya's mother...at least that would make the most sense...since she was so concerned about Kouga.

Of course, that would mean, technically speaking, she'd have to have been pregnant with Byakun when we saw her...

Do they even get pregnant in Soul society? That's something I've been wondering XD (sorry for the random thought tangent)