I have a few suggestions, but I only have the general idea of these suggestions in mind.
One idea I had was the C support between Xander and Nichol, where Xander questions Nichol why he got mixed up with a bunch of Ruffians, and Nichol explains that Xander arrested his commanding officer, which caused his squad (or battalion? what would be the medieval equivalent be?) to disband, leaving him with nowhere to go. I know this is a bit of a creative liberty, but I was thinking that Nichol's former commanding officer could be Hans. I was thinking that it'd be similar to Henry's relationship with Mustafa before he died in Awakening, and I think it'd be neat to tie Hans into Nichol's backstory.
Another idea I had was a Kotaro paralogue, where you find Kotaro talking to some villagers who are freaking out because a group of Faceless are approaching their village, and Kotaro says that he'll take care of the Faceless, and goes to take care of them, thinking to himself that once he takes care of the Faceless, he'll exploit that village later. And during the chapter, you have the Avatar talk to and recruit him, and then, once the battle is over, he decides to stick with the Avatar's army, and then thinks to himself that, since he didn't exploit that village, he felt something, and that it felt good. It's only a basic idea of the paralogue, and I'm very tired. I did however think of something cool, if you have Saizo talk to Kotaro, Kotaro would become an enemy, and you wouldn't be able to recruit him. Or maybe you can still recruit him, but it has different dialogue.
I think Kotaro's personal skill would either be Shuriken Mastery or Grisly Wound, and I think his secondary class set would either be Spear Fighter or Oni Savage. And it would be a crime if he couldn't support with Saizo, I can see his supports being similar to Matthew and Jaffar's from Blazing Sword.
I probably overloaded you with these suggestions. XD
NOTE: I tried to PM this to you, but it said I couldn't initiate a conversation with you.