Here's the basic idea. The characters would all be modern-day anime harem versions of Sengoku-Era historical figures. They would be working for the redoubtable and implacable yet remarkably naive Oda Nobuhina, aiding her in her overcomplicated attempts to conquer the world and set it to rights, and generally spending most of their time fixing the messes she makes in doing so. I'm thinking a predominantly female cast, though with at least one or two lucky hapless males in their midst. Think along the lines of series like Battle Girls: Time Paradox, The Ambition of Oda Nobuna, and especially Sengoku Collection (Parallel World Samurai).
For systems, we'll probably use either OVA or BESM whichever would suit the group better.