I never did finish the first season of Sekirei. Part of the reason I lost interest was that I never did get a grasp of who everyone was.
But the first three episodes of this second season have been entertaining enough that I want to know who everyone is and how they relate to each other.
So to start with, I've made a characters/seiyuus page showing pics of 26 characters and their seiyuus, with a bit of info about each character and seiyuu. It helps me. I hope it may help you.
Click here or on the image to go to the full page.
There is more detailed info about each character and about the overall plot on Wikipedia, especially on that site's Sekirei characters page.