Turns out there are parts of the Nohr story that don't make any sense unless you played Hoshido first. And on top of that, both the Hoshido and Nohr stories are part of some kind of time loop. The third path DLC is about breaking the time loop by unitiing Hoshido and Nohr against the true enemy, the "invisible demon kingdom", I s--- you not, and is undoubtedly the canon path.