Sorry for the sudden change in style, I originally wasn't planning on combining these but.... it's just more practical this way!
In Basara 2 you see Kotaro serve two different camps, and in Basara 3 he's back to fighting in the name of Hojo only.
I set it in my mind that Kotaro's a pretty loyal guy. Maybe Ujimasa owed Hisahide something and said, "Kotaro, go and clear my debt with this man, else the glorious name of the Hojo clan will be tarnished...!!" - who knows!
Anyway, these are my resulting thoughts on Basara consistency.