You need Takeda Shingen of Kai, and then another Takeda Shingen of Kai, and then, for variety, yet another Takeda Shingen of Kai. Once you have several of them--and I mean several level 55 versions so that you can inherit all but one, not just several that you merge into a single four star version--then you can look at Sanada Yukitaka, Naoe Kagetsuna, and Imai Soukyuu.