I would have killed for a Shura x Saizo/Kaze support (either/or), maybe something about the history of Kohga and the Moshukujin.
Scarlet and Ryoma support should have happened, or at least in Birthright. And Reina should have at least been able to support Mikoto's other retainers.
Fuga, he should have also had a support with Ryoma, to talk about Sumeragi. Yukimura doesn't do much except talk about strategy, but at least give him some supports so he doesn't seem like such a two-dimensional character.